I put hook and loop tape inside.

2 1/4 inch square pads on the plastic electronics cover, all the way in the back, and one 1/4 inch square pad in front of where the suspension bars snap in. Then i put the loop pads inside the body after it's painted, and tried to line 'em up as close as possible. My HO Scale body was actually too short. If you look in my photos you can see the back end of the motor bracket hangin' out.