The spanish dude working at the car audio shop said it was bad to put this, but his english wasn't the best so I don't know what he said exactly.

I want to put something like this, with the sub amp hidden in the kit area (in the 96 it has 3 tabs that you flip to open it up and it exposes the jack and wrench and instructions)

I want to do this so i can just unplug the wire from the spare tire kit and take the box out in seconds instead of having to get a screw driver and un-screw the amp hookups or unscrew the sub terminals (putting them back in is a pain as well)

Would heat be an issue?

I can easy put a 120mm fan in there if needed, but could use some suggestions on that.

 

heat will be an issue. It will need to have proper cooling. Also, if your encosure isnt secured to the vehicle (not just velcro'd or bungee corded in) it will be a missile aimed at the back of your head in an accident. If you dont think it will kill you, you are a fool.