The point of my post is its a bad idea, no matter how many people do it. Only a novice would think its a good idea.
Think about it this way. Every time the sub hits it puts pressure and vibrations through the box. Do you really think that is good for an amp?
I know people who have had several amp failures, and all had the amp mounted to the sub box? Coincidence? Possibly, but I have never mounted an amp to a sub box and have never had an amp fail.
Yeah, cuz your car doesnt bounce and shake around driving or vibrate when the sub is loud anyway.....