Yeah, the box is constantly vibrating and flexing whereas the amp is not...the stable/unstable environment causes amp components to shake loose and ultimately you lose a great deal of potential life on an amp. Normally, you can just mount it to the car somewhere next to the sub, or get an amp rack if space is a problem...
yeah dont mount on the box. i like to mount mine to a piece of wood then mount the wood in the trunk in a nice location so i can get to the gains and others. just make sure you mount it so it can cool good