Moisture, thou art mine enemy!
February 22, 2011 7:06 PM   Subscribe

I'm going to build a camper shell for my truck and need advice on how to seal/paint it to protect it from moisture.

I'm most comfortable working with wood (which isn't to say I'm an expert) so I'm going to build a frame from natural wood and then use some kind of plywood or MDF over the frame to enclose it.

I'm interested in what everyone thinks would be best to seal the manufactured wood itself, and to seal the joints between the pieces.

One thought I had was "rhino-lining" or a similar "rubber" coating that is used as a spray-on lining for the cargo bay of a truck. Would that work sprayed onto wood?

I not looking forward to building windows, but I think some kind of ventilation would be a good idea. What would you suggest instead of glass panes? Maybe panels on hinges that I could prop open. How would I make them waterproof when closed? Weatherstripping?

What about insulation? There are spray-on soy-based insulation who's positive points are being green and seeming easy to install. What are the negative? Thanks.
posted by gregg to Home & Garden (14 answers total)
I don't have answers to your specific questions, but I can recommend the Expedition Portal forums as a source of information. Check out some of the build threads to get an idea of what construction techniques people are using.
posted by jackmakrl at 7:46 PM on February 22, 2011

I have another brand of "rhino lining" in the bed of my truck and it's pretty goddamn waterproof, best I can tell.
posted by notsnot at 7:53 PM on February 22, 2011

From this description it is kind of hard to understand just what you are trying to do, but... I would make sure all joints over hang lower pieces, like this. Ideally you would want a slightly pitched roof. If you cannot make the roof out of one piece, then the higher parts should overlap the lower. Caulk, caulk, caulk.

Hatches should be under an overhang. You can make them seal with weatherstriping gasket. You might want to look in a boat store for good hinges and latches for them, as well as other waterproofing stuff. Being water proof is very important for boats.

Good luck
posted by d4nj450n at 7:58 PM on February 22, 2011

MDF is the wrong material -- it's heavy, not very strong, and crumbles when it gets wet. If you are set on using wood, I would think you would want a fairly thin marine plywood, covered with some kind of marine varnish or epoxy-based waterproofing. Basically, if some hobbyist can use it to make a crazy wooden rowboat, it will work great for your truck. Equally, the construction techniques that work for wooden boats (emphasizing strength and lightness, will work for your truck.

At the end of the day, though, you are likely to spend more money (and a lot of your time) to build something that is heavier and less useful than a standard aluminum or fiberglass shell.
posted by Forktine at 8:14 PM on February 22, 2011 [1 favorite]

I was thinking marine applications as well. Specifically, fiberglass over the wood.

You will need several coats of fiberglass + epoxy hardener. This stuff is TOXIC to work with, so suit up, use gloves, and plan for good ventilation!
posted by jbenben at 8:28 PM on February 22, 2011

Oh if you do use fiberglass, you need uv resistant epoxy or polyester resin.
posted by d4nj450n at 8:40 PM on February 22, 2011

I'd use "Grace Ice and Water Shield" over the plywood. Then side it and roof it as normal, over the ice shield... Nothing gets past bitch-a-thane!
posted by Glendale at 9:05 PM on February 22, 2011

I built three chicken tractors last year before I finally made one that worked. It has come through a Pacific Northwest winter quite nicely.

Along the way I tried both MDF and that super-thin plywood (called "lauan"). The MDF got soggy and kind of dissolved. The super-thin plywood did what I was told is called "potato chipping," where different layers absorb moisture from the air at different rates, and it curls up and destroys itself.

This third chicken coop is built out of construction-grade exterior plywood. Exterior plywood is meant for outdoors use, so it's a bit heavier, and a bit more expensive, but totally worth it. Here's a rundown on plywood types.

Once it was assembled, I coated it with timber oil (leftover from staining my cabin). It has kept out the moisture quite nicely. (And it makes the henhouse match the people house, which pleases me.)

I don't know about caulk, because you can't really use it around chickens.

Rhino lining is awesome, and totally waterproof. But I think the expense will probably negate any cost benefits of making a DIY shell. (I assume you're building it yourself because of cost.)

Making weatherproof windows is going to be tricky. I say this because I made several different kinds of windows and openings in the henhouse along the way, and they have been problematic to say the least. Currently I have weatherproofed them by cutting open a feed sack and stapling it over the frame. OMG SO WHITE TRASH IT HURTS. I have yet to figure out "the right way to do it," although I swear that I will once the weather is nicer.

In other words, I wouldn't try making windows unless it was absolutely necessary. It depends on what you're going to be doing back there. If people will be riding in it when the truck is in motion, then yes, it is absolutely necessary.

If you're going to be camping out in it, then I would probably take a "wait and see" approach. Frankly, no matter how tight you try and seal it up, it's still going to be a bit drafty. Probably enough to dissipate any condensation that might accumulate overnight when you were sleeping.
posted by ErikaB at 9:06 PM on February 22, 2011

Like Forktine or jbenben, I would fiberglass it. Unlike jbenben, I would use only a single layer of fiberglass, since you really are only looking for weatherproofing here, it's not going to be submerged for long periods of time and it's not going to be bouncing off the bottom of a bay or dragged up a beach.

Epoxy is actually not particularly toxic to work with, but the older (and much less expensive) polyester resins are. Epoxies for this application can cost in the neighborhood $100/gallon.

Two of my hobbies are building surfboards and restoring old boats, so I might be biased in favor of marine-like solutions. My uncle once built his own camper shell and used a wooden frame with some sort of corrugated aluminum-siding-type sheet metal over the top as the roof. It worked fine and lasted for decades.
posted by tylerkaraszewski at 10:29 PM on February 22, 2011

Forktine is correct in saying MDF would be a bad choice, it should not even be used indoors where it might be exposed to moisture. There is a ply product called MDO (medium density overlay) which would work. It's meant to be used outdoors (it's used for highway signs) and takes paint great. If I were to use that I'd apply it over a 2x4 frame with stainless screws.

I'd caulk the seams with 3M 5200 marine adhesive/sealant. This stuff has a long cure time (the fast cure version takes 24 hours) but can be used for underwater applications and stays flexible which is important as you'll have a lot of structual movement.

Home Depot carries the 3M 5200 at about $10 a regular size tube (if you go to a marine supply you'll pay twice that) and for the MDO I'd call around lumberyards for pricing. I think a 1/2 inch sheet runs a little over $20. You would not want to go any thinner the 1/2 inch. Of course you could use exterior plywood but it won't look as nice.

I also agree with Forktine in that you might be better off getting a premade fiberglass cap that already has windows and vents that seal tight. After pricing out all the materials (wood, screws,paint,hardware,caulk) you might be pretty close to a premade unit.
posted by PaulBGoode at 10:55 PM on February 22, 2011

Rhino lining and other truck bed coatings will stick to plywood well; they are also hellishly expensive.

Best thing for venting windows if you need actual water tightness (many canopies aren't 100%) is RV windows. Look around for a wrecker in your area to get them cheap. Non venting windows can be as simple as lexan in an aluminum channel sealed with sikaflex sealant.

I made a cargo conversion for my car trailer (IE: a big wood box that converts it into a cargo trailer) out of 3/8ths plywood and glue lams approximately equivalent to dimension lumber. The roof was sheathed with an MDO like 5/16th plywood and then coated with mobile home roll on roof coating (red 'cause it was on sale for half price). After four years it is still in good shape with no leaks, delaminations, discolourations or really any noticeable difference from day one. The roof coating is commonly white or silver but is available in dozens of colours if you ask around and starts around $20 a gallon which two coat covers about a sheet of plywood; maybe a sheet and a half.
posted by Mitheral at 1:40 AM on February 23, 2011

What you want to do is build a wooden boat. Boats are light, structurally strong, waterproof, and there are a ton of resources out there on how to do it in your garage. Your trick will be designing the boat so it fits and functions as a camper shell... which is probably a lot easier than designing a boat that handles well as a watercraft.

In short, use home boatbuilding techniques, and you will have a camper shell that works awesome and looks like a million bucks.

Stuff to investigate:

- Marine grade plywood: Lightweight, durable, easy to work with.

- Glassing, or fiberglass covering: transparent, strong, watertight, repairable. You're applying a thin fiberglass coat to a plywood shell.

- Hatches and port windows: these will be your windows and skylights.
posted by Slap*Happy at 6:29 AM on February 23, 2011

I think you need to take a two pronged approach. You have two different problems: surfaces and joints. The rubber Ice and water shield mentioned above is excellent for sealing corners and seams. I would imagine that a combination of exterior grade plywood and a waterproof sealant like the Rhino would work for the rest. I would test how well the Rhino coat adheres to the rubber ice and water shield before committing to it though.
posted by Gungho at 8:38 AM on February 23, 2011

Definitely what Slap*Happy said. Google "Stitch and Glue" boat construction. The biggies in marine epoxy systems for stitch and glue are System 3 and West.
posted by klarck at 6:16 PM on February 23, 2011

« Older Planes, Trains, and Automobiles...   |   Illegal price fixing or good business? Newer »
This thread is closed to new comments.