It's the same argument for when people strap their amp to a box. There's good installs and bad installs. Everything should be secured in place if making final connections. Even just driving adds vibrations to the amp. The vehicle is a poor environment for this equipment already. If that proximity causes problems, what do SPL guys do with their amps? You're talking 150db's on the far side of the vehicle. Not 120 db's in front of the speaker like most typically output.