I have a plywood box in the back of my pickup that holds long stuff (tripods, prism poles, digging bars, shovels, long stakes, etc.). It has stood up well to the loads I've placed on it, but after almost 15 years of exposure to the weather it's falling apart.
I'd like to replace it with an all-aluminum box for reasons of durability and appearance, and maybe even some weight savings. However, I don't know how thick an aluminum top I'll need to obtain the same kind of performance I've gotten with 1/2" plywood.
The current plywood top spans openings ranging from 10" to 18", and it hasn't balked at being jumped on or having sacks of concrete and sand stacked on it. I'll need the aluminum top to do the same thing. Since I'm interested in saving weight and cost, I'd like to find the sweet spot between weight/cost and a top that's too thin to bear the load.
Is there a formula that would allow me to size the aluminum top for this application, or is this a seat-of-the-pants/try-it-and-see/if-at-first-you-don't-succeed proposition?