Sub box behind seat - available space?

[ItWillBeSlow]

FirstC10 and 1971Stepside - I have a question for you guys, and anyone else with a similar box.

How did you build your floor for the box? Is it a piece of MDF resting on the rear "ridge" with some feet under it to support at the back? I have aftermarket cab mounts and an extra nut (original nutserts are stripped), so my cab bolts/nut extend above this ridge. This means I may need to raise my floor about 1" to clear the nut. I could double the bottom plate and cut a hole in the bottom one to clear, but wanted to see what you guys have done.

Regarding the clearance for the OE bench I started this thread for, it seems the back of the bench is basically a straight line from the rear seat bolt hole to the rear of the cab where the seat touches. I should have plenty of space with this sub (JL 10 TW1). I'm planning to offset it to the passenger side and use the driver side for storage.. i think.

Pictures probably do more justice than my descriptions! The level is roughly the back of the seat.