[Jack Bauer]

I personally like putting it under a front seat because it will get
better air flow there and also not get in the way of things like it can
in the trunk.

The trouble is that so few amps are small enough to actually FIT under a
car seat. For some reason everyone thinks they need 100W/channel. I have
an old Sony that puts out 20Wx4 and is quite small enough to fit;
although as I go forward with a newer car it becomes hard to find
something new that small.