I actually wanted to see pics of where you mounted the amps.. nice setup though.
i mounted it on my back seat...drilled through the metal backingthey will be fine on the back of the box. just mount them on rubber feet or something to dampen the vibrations, and you will be fine.
i dont give a **** as long as its loud and doesnt catch me on firelooks really crooked, i would put a board inside the back of the back seat, where you are mounting it, and then screw it to that. and make sure its level. with that nice of equipment, you dont want it looking like sh1t.