From the extended cab show ur pics thread:
This option also give you the use of both seats if needed.
Putting it directly on the floor would help. Then you'd have two options for the amp. 1. Under a seat or 2. Mounted to the rear wall. Of course if you've seen the floor box I built in mine, you could do a half sized version of that to mount the amp in (Or platform to put the amp under) and bolt the box directly onto it or with brackets.
Do you use the other rear seat? If not, consider the floor platform I and several others have built. Works great for me!
Hope this helps,
Bummer it's not an 8, you could cram it in the rear door....