Well, you may need to define "cold" nights, but for the record, LP is said to stay liquid at about -40*, so the closer that you git to that number, the less evaporation that you will git. This is why most wintering tanks are "lay down" tanks, as that allows much more evaporative surface in the same size tank.
I don't know if they offer lay down tanks that are of camper size?
But I think that you could git away with a 120gal tank if it came to that.
I think that is the largest tank that you can legally move when full.
Another option is if you could tie 2 or 3 40# tanks together?
I have seen this done on larger (V-8) fork-trucks, but those draw liquid, not vapor, so not 100% sure that it would work, but I don't see why not?
This would get your surface area up to a point that might not choke?
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