Mount the amp up on wooden blocks first of all. Second, get some computer fans and find an acceptable way to mount them (ie, not duck tape). If you are careful, you can screw the fans to the amp, but you MUST know what you screwing into. There is usually a few spots were it is safe to screw in without hitting anything, but it requires you to take the amp slightly apart, look, and mark. Personally, I would build the fans into the wooden blocks/stand for the amp. Easy, reversible, and no chance of screwing up the amp.
Now, as for the fans, you have a couple options. 12V fans and power them from the battery (install a kill switch, or wire them into wires that are live only when the key is in ignition or acc). A different voltage fan can be hooked up to the appropriate batteries batteries (can get messy if the batteries crack open or corrode, but you can build/buy a case for them too with a kill switch). Computer gamers know a lot about running auxiliary fans off of batteries. Might want to look in that direct. I'd jut wire in the car battery, but that is a lot of wiring. Separate batteries would be quick and simple, and much less permanent.