Part of my need to build my own box is because I have a need to transport something very large, and the commercial boxes on the market will not cut it. While some of them are quite big, they will not fit a Sig Kadet Sr model airplane with a 6.5' wingspan. The cargo box will also do double duty for hauling all the family stuff when we do road trips, so its a win-win.
When I started doing my research on DIY cargo boxes, I was surprised to find that basically no one has done this. I did find one company selling plans for a DIY cargo box, and their examples were gorgeous. Alas, they would not fit my needs. In all this internet hunting though, I found lots of plans for canoes, kayaks, paddle boards, sailboats, skiffs, trawlers, etc. This got me thinking, "If all these boats exist, and are strong enough for motors and/or the ocean, why not use some of these techniques for a roof box?" I also remembered that my brother had built a camper top for his truck out of foam board and fiberglass, and when I asked him about it, and whether foam board was good enough, or if plywood would be better, he thought plywood was the route to go. This got me back onto the stitch and glue track. It also got me interested in doing this project as a primer for the next project, which will be a paddle board to replace my broken windsurfer board.
When I found the plans for the Ta'al Touring paddle board, I saw the shape of the board and read the description and instantly though, "Wow, this guy knew what he was doing." In his description of his board, for which he uses 3mm plywood, he references Moth dingies. These are some of the first hydrofoil monohulls in the sailing world, and most were home built from 3mm or thinner wood. These boats also take a lot of abuse because they are flying above the water, and sometimes unceremoniously plunged into the water at speed. This is a lot of force and stress on all of the hull, but these boats continue to chug along.
With this in mind, I wanted to build my box as lightly as possible. Yes, I could have built it all out of 3/4 inch plywood, and it would have been fine. It would have weighed like 100+ pounds, so it would have been a struggle to get it on the roof, would have killed MPG's, and would have left little weight capacity for planes, bags, or other freight. Also, with material that thick, it is difficult at best to get curves that even approach aerodynamic.
