curve a flat piece of 1/8" x 1 or 1-1/4 into a u.weld bolts or studs to it to replace the u-clamp you are presently using.it wont pinch the frame.over kill would be 2 front and 2 rear.then you would need a taller mounting plate with more holes.
i was planning on using small muffler clamps,my frame is steel,so i welded.