In my reg cab F-250, i pulled down the carpeting going up the back of the cab, and glued a piece of 1/2 in plywood to the back of the cab in the resesed portion. Then i put the carpet back over it. Now i can mount anything i want to the back of the cab with short wood screws.

 

good idea, just make sure u used strong glue cuz amps are heavier then u think and might fall when it gets cold and hot with the amp cooling and getting hot. also make sure u have plenty or open space around the amp. in fact i might try this...