12mm or 18mm marine grade Birch plywood seems to be the choice of professional cabinet builders. As this is scale version, 12mm wouldn’t be practical. I found some 3mm ply in the garage, which is “correct” for a 1:4 scale version.
I’m trying to build a cabinet based on opened back Mesa 1×12 wide body cabinet. When finished it should be approx. 14cm wide, 10cm high and 7cm deep.
Next time I would not put the back panels where I have. As this is a straight fronted cabinet, the first 4 cuts are all the same width. Instead I would put the real panels in the same line as the speaker baffle, as they should all line up (and the space to cut the batons from).