I want to build a wooden box of size about 16 inch height x 24 wide x 20 long. It is a return air plenum. The "box" will not have a bottom (where the return air duct is) and no front (where the grill cover is). Right now the entire wall cavity is the plenum but I need to clean it up. If you want to know the details you can read my previous post.
Should I use 2x2 or L brackets to screw the wood panels together? L-brackets seems easier because I won't have to drive long screws through a 2x2 inside a small wall cavity. But I also feel using L brackets is not as good as a
2x2.Also, what thickness wood panels should I use? 1/4 inch plywood seems strong enough. However they tend to warp a little over time. If the box is held together with L brackets (say two brackets per edge), warping could create unwanted gaps. 1/2 inch plywood would stay straight, but seems overkill. I see some material call hardboard that is 1/4 inch think with a vinyl coating. Could those be used?