Sides will just be single layer of 2x4's, which is really solid. Back wall is two layers of birch and one of 2x4's. Bottom is just going to be two layers of birch, but it's covered with 1/4 inch of resin and cracking the resin with a hammer was hard to do when disassembling the last box. Top will be a layer of 2x4 and birch. Front will be two layers of birch and one of 2x4. Internal bracing will be 1" threaded pipe and more 2x4's.
I am actually going to brace the inside too
Thanks, it is extremely solid.
I have only used 16 out of the 50 2x4's I bought and both sides are done. I'm not going to run out. Definitely easier to use 2x4's than a bunch of plywood layers, and cheaper too.