The only way this can be done any way is for the box to be mounted to heavy frame, you would have to look and see if there are adequate mounting points on reinforced metal and adding that kind of weight to a stiffener in the ceiling is asking for rippling of sheet metal. I would say this is an option for a show vehicle but for a daily driver it would be ill advised. Anything you can do to make the enclosure lighter would make this feasible (remember the sub is now inches from your head so it will seem loud!). I would say mounting amps in the ceiling is certainly doable (and has been done) so this is do-able too but I am not sure it is wise... depends on the mounting point and the overall weight.

 

This sounds like a really bad idea x_x

 

Thanks for the input gents. I think I'll abandon the idea for now. Too bad cause there is a lot of room above my head. I'll stick with plan b and use it for some good sound dampening up there instead. Stuff that sticks well to a tin roof and could hit me at a hundred miles an hour an ot hurt@!@