yeah, i dont think you should worry, I have had lots of amps on lots of boxes and never had a problem. Maybe if you box is flexing and you are running like 2k+rms then it might be a problem but anything other than that should be ok
the vibration thing, i don't believe in that. i have 2 1550ds mounted to the back of my enclosure. nothing so far. actually i've had all my amps mounted to the box except for 1 setup.
i doubt that if your box is built well vibrations will not be a problwm but IMO if you mount an amp on the box its just like a package deal for a thief so i mount mine behind my box ... in the trunk but i have 3/4 MDF lining my trunk floor, i also mount my sub box from the inside with bolts