This will be an oddball but I've decided to start running numbers for a temporary and cheap passive horizontal closed loop just to help keep a 5th wheel camper from freezing on the underside. It is already skirted with plywood and foam board with spray foam seal. It is not really ideal but thought I might try this. I have plenty of poly pipe around, on large acreage, and have a very large excavator so digging the loop in is a minutes type job. My thought is to run a slinky underground, then bring up the two legs near the camper and run another slinky under the camper. This is in Kansas and we touched -10F last year, but that is really rare. Rare enough the ground even at 5ft would not have been even close to that. I want to just install a 12V circulator pump and move some Glycol around and see how this passive thing would go, but I will need to make some assumptions on heat loss/gain here. I know the pipes would freeze up last year at about 15F ambient last year so I would guess air temps are in that 25-30F range down there. My thought is if I can get big enough pipe in so I can run a pretty decent flowrate, maybe I can get the math to work assuming around a 55* ground temp. Thoughts?