hey i just installed (by myself, that might be the problem) a sony cdx-gt740US stereo on my car, but it gets to hot in the rear, i dont really know the normal temperature of a working stereo haha
my JVC gets hot too. how did you wire it up? if you're sure that the wiring is correct then don't worry about it.
is it shutting off? if not then your ok. if it starts to shut down due to heat then you can add a small fan behind it. i had a head do that many many years ago,and the fix was the fan.
It depends on how long you want the equipment to last. Heat is the enemy. Each of the hundreds of components in the stereo has an AFR (failure rate) that is proportional to the temperature of the part. A hotter part has a higher failure rate. If the part can be 10°C cooler, then the AFR is 2X better. Cool fresh air is the best option.