I usually like to hide my bolts on my builds, so I weld nuts inside the frame for body mounting before I box it. I went to an industrial rubber supply company ahd bought a sheet of 4' by 8' 3/16 th inch thick rubber and had them cut it into 2" wide strips. I then build the body sub frame for the body so it sets on top of the frame rails. the rubber strips are glued to the frame so it sits in between the sub floor and frame. I made a punch out of a piece of 3/4 round tubing to punch the holes through the rubber. I has worked for me on a few builds. What have you guys done.