Shane Speal & many others use hot glue under the lid of cbg’s, it seals em up proper? Boxes with warpy tops could be somewhat of a challenge, I usually screw those stubborn corners down after gluing them, it’s worked so far, knock on wood :) good luck on this, let us know what happens :)
Personally, I set pillars in the inside corners and screw to them (though I am far from expert). I also screw the neck to internal support blocks.
I didn't close it yet to be able to further manipulations, but I think I will stop here and try to screw/glue it tight and see if it changes it's sound, I'll keep you posted