Buyers salt spreader mounting ????

Hey, I recently bought a buyers salt/fertilizer spreader for my 2004 660. I don’t have enough posts to attach a picture but, it is the 15 gallon spreader that buyers makes.
My question/concern is that when I mounted the spreader on the back it started to bend the rack, and there wasn’t any material in the spreader, just the weight of the spreader was bending it. If I didn’t carry salt bags on my rear racks I would just put some ratchet straps on it. Does anyone have a suggestion or fix for this issue?

Thanks,
Patrick