I put my amp in the hump inside the trunk (to the left of the spare tire). No screws needed and it comes out when you want it to. The only concern is it sits where the fuel pump (i think) wires are. Never has moved or caused any huge problems.

 

Mine is under the drivers seat.
Darcy

 

hossman: I have a 4 channel amp mounted behind the passenger seat. It's mounted horizontally and just fits.
I have had issues with overheating on long drives combined with the passenger seat positioned all the way back. This issue was solved by moving the seat forward by an inch to give the amp a little breathing space. No issues ever since.

 

That's sort of where mine is, except mine is screwed to the bulkhead. Mine's a 4 channel with the two rears bridged for the sub (took out the tool tray), and I'm getting overheating problems now that it's warming up. I plan on wiring in a computer fan. Also, I'm getting a monoblock amp for the sub, and using the 4 channel for L/R woofer/tweeters - upgrading head unit to one that uses active crossovers. I plan on mounting the monoblock to the left of the current amp.

Only complaint with mounting the amp up there is I can't fit my acoustic guitar hardcase in the trunk anymore, as the amp juts out just a little too far to clear the body of the guitar.