Welcome back iveseenbetter. I thought about this
post with images from a PSB owner's thread.
Yeah, makeshift box will probably resonate big time, besides the reflective issues. The above pics use insulation, which I think could be key. Maybe the above could give you ideas.
I don't know what your brackets are like, but I wouldn't worry with my huge one. Then again the brackets I use have two screws a piece.
As for the subs, the first thing I think of with kids are hidden toy cars in the
ports.