if your in the desert or somewhere without snow that works,but in the winter youll be tracking mush and ice onto your amp and amps LOVE water

Or next to your subs so they are out of harms way and aren't getting kicked around and you don't have to hide as many wires.

for my car im lucky enough to have a flat location that isn't directly against the subs and that is close enough to a good ground w/o having to worry about people fucking with it

Yeah, but then you also have to run a really long wire to your subs.

Your amp should be mounted near your subs, but never, ever on the sub box itself.

^^

What u guys think of mounting my amp on the back of my back seat?

I think its fine if you use an amp rack.