Is your car 3dr? You would be best to build an enclosure around the amp if you did, so you can put fans in it, otherwise the static air may get too hot for the amp, and cause it to over heat,
Autoaucustics(sp) do an amp box that fits into the side of the boot perpendicular to the floor, so only uses about 10cm of floor space, have a look on there website, sorry cant remeber it!!!