Please tell me your sub box was then bolted to something other than your moving floor... You
do realise how deadly 50-100kg of subs is at 100km/h (or much, much more), don't you?
I hope everyone else here does too... a sub box doing 100km/h when your car hits something will easily take out your rear seats (including any passengers) and most likely proceed to fly out the front window, taking everyone in the car with it, and not necessarily in one piece. I've seen this happen, and it's not fudging pretty :/
A hinged floor IS a good idea though. I was considering making a wooden floor that is hinged at the base of the rear seat AND in the middle of the floor itself, so when you open it, it folds like /\ <-- that. I reckon that would be schmick
Astaroth.