I bought a 2 1/2 or 3 in. sq. tube (I forget), capped the ends and bought some two in. wide, 1/4 in. thick angle iron, made a "tube" to go around the frame rails, and that gets bolted in with three grade 8 bolts on each frame rail. The bottom angle iron can then be drilled to mount the hangers. I moved my shackles forward a bit to increase travel, too.