I mounted mine under the bed, just behind the cab on the drivers side. There is a bracket that the bed rests on and I hung it off of there. (note according to the manual the firestone compressor model I have can be mounted upside down.) Next I built a box (16 ga steel) to go over it and keep rocks etc away from it. Also farther back on the same side I mounted a 1 gallon tank and enclosed it with a box.
Good luck
George