Ex Cab silverado amp install location

I recently added an after market system (front and rear) along with a single 12" down-firing sub under the rear seat (driver's side); along with two amps under rear seat on the passenger side.  Everything works fine accept the amps are in plane view once the passenger rear door is opened.  I'm trying to keep this looking as factory as possible as well as minimizing the view of any components; which is why I kept the factory deck and went with a down-firing sub.

 

What I am curious about is how common is it to mount amps to the rear of the cab behind the rear seat back?  How do most mount them?  Mount a carpeted piece of MDF to the cab and then the amps to it or just mount the amps to the sheet metal?  What type of fasteners are used and should the screw holes be sealed with silicone?  Obviously, it would be difficult to get a wrench between the cab/bed so are self-tapping screws OK?

 

Thanks in advance for you guidance!