Our 39' MH was dragging going up the drive, too, so I ordered a pair of these:
http://www.amazon.com/gp/product/B003YJPG26?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00These were smaller wheels than the narrative recommended for a MH of that size but they work just fine. I bolted them on the trailer hitch, as far out to the edges on each side as they would fit. Work great. They actually don't carry that much load when you think about it. Just enough to push the rear end up a little bit. And, that load is carried for a very short time.