DIY Truck cap - steel or aluminum?

[RIPbiker13]

Hello all, first time here. Super cool site and I don't know how I haven't come across it before.

A little bit about myself, I fabricate and weld and have a YouTube channel related to my projects. Currently, I'm restoring my dad's 1969 Ford F250. We also have a 1974 Holiday Rambler bumper-pull trailer. I did a lot of work on it and lived in it for nearly a year. It's currently in storage. My F150 did not like pulling it and it wasn't as portable as we had hoped. So we just bought a 2017 F250 and will be getting back to using the camper.

In the mean time, we have two dogs, and two children, so the truck gets very cramped. We would like a cab for the bed to keep the dogs safe while traveling. Caps are VERY expensive and I am not finding much in the way of used, but I'm looking. So I got to thinking, I make a lot of other things, why not this?

My thought is a steel frame using 1" square tubing, three ribs front, center, and rear, running from the driver to passenger side and a couple pieces to connect them front to back, then skin the frame with 18 or even 20ga sheet metal and stitch weld it for strength. Weight isn't a huge concern on a 250 and I don't think the weight savings would be significant between steel and aluminum on the small scale of this project, but I've been wrong before. Also, I don't have the ability to weld aluminum yet, so that would be an added cost to get the right welding gas.

I would like to remove it when not in use regularly so it would bolt in when attached. Insulation is a concern because building a metal box would get very hot inside. LED lighting is a simple matter and I was thinking that it it were steel, it would be strong enough to support a rack for my kayak for those fishing adventures too.

I'm fairly certain there is something I'm over looking and failing to consider. Any input, ideas, advice, anything, would be very welcome. Thanks for taking the time to even look at this. Again, super cool community here. Glad to be here.

 

[ckelly78z]

Welcome to the forums. I too do many home building projects, and like the way you think.

Have you considered using corregated metal barn siding for the roof, and side walls of your new cap, then you could use the self sealing (waterproof) roofing screws that have the little rubber washer on them into some 1x1 tubing. There is also foam runner insulation strips available that has the corregated shape to it so it wouldn't rattle.

 

[RIPbiker13]

Welcome to the forums. I too do many home building projects, and like the way you think.

Have you considered using corregated metal barn siding for the roof, and side walls of your new cap, then you could use the self sealing (waterproof) roofing screws that have the little rubber washer on them into some 1x1 tubing.  There is also foam runner insulation strips available that has the corregated shape to it so it wouldn't rattle.

I have considered that and have plenty on my property, but the material I have is old and I cannot weld it. The screws are a great idea and had thought about that, but with the old material, it is also full of holes. I have used some of it to build the wall in my shop. Not sure about the execution however. My thought is stretching thin and smooth sheet metal is easier overall than corrugated metal. I'll likely be building the entire thing by myself, with my wife helping if I really need it.

 

[Gr8ful]

I'd use smooth steel not alum as steel is stronger & if alum gets urine on it will eat holes right thru it. You can't use alum in livestock buldings as the fumes will eat it also. They make a pole barn steel they call galvalume which is steel but with some alum in the coating, that you can't use eith just bare or better yet painted galv steel. Good Luck!

 

[tx2sturgis]

If you just want to build a cap that is lightweight and easy to remove, why not frame it with 1" aluminum square tubing, tubing connectors for the corners, and then rivet or screw aluminum sheet or FRP resin boards as the outside skin. You can drill and then rivet or bolt the connectors. 

Doors, vents, and windows would complicate it a bit, but can be integrated into the design without too much trouble. 

Building a simple box, with 90 degree corners everywhere, could be an easy weekend project. 

If you are willing to spend the money, look into ARE DCU toppers and caps. They make good stuff.

 

[Weldman]

Aluminum is third the weight of steel in same size for structural strength, aluminum tends to crack from fatigue faster than steel and mixing aluminum with steel causes electrolysis that will eat through the aluminum eventually. I personally would frame with steel and sheath with wood or FPR as to break the thermal bridging. You can only shove R6.5 per inch of closed cell spray phone insulation in walls and runs about $1 give or take few pennies per board foot. Welding aluminum isn't that hard it's more of cleaning than welding that gets people in trouble, as there is proper way and if you do take on aluminum please do not use chlorinated brake cleaner it will create phosphene gas that will kill you. Lastly majority of motor homes are framed with 1.5" steel tubing with around 14 gauge.

 

[AeroNautiCal]

As has been said, FRP or wood would make for a straightforward construction process, as would your proposed use of very thin sheet steel.

Likewise, corrugated sheets of polypropylene would be light, robust and easy to work with. 

As for the question of overheating the dogs, perhaps consider fabricating a second roof covering with an air gap in between (as seen on Land Rovers used in very hot climates).

Obviously, in conjunction with adequate insulation in the entire main canopy.

 

[flying kurbmaster]

I would be patient and keep looking for a second hand one already made up, perhaps start looking in the back yards usually lots of those things sitting around, run a wanted add, check out the local junk yard, someone has one sitting around just around the corner somewhere.

 

[JD GUMBEE]

^^^What FK said. Yep.

You cannot find a decent fiberglass with slider windows? Lots cheaper than the home made deal will end up costing.

 

[highdesertranger]

I agree look for a used one. highdesertranger