I have a North Face Ember synthetic bag made with Polarguard 3d....
Have had it for years and store it unrolled at the top of the closet. If you are running out of room in the van, perhaps you could keep it unrolled on the very top of yopu other gear, but then you'd have to move it every time you wanted to get something under it. Or just store it compressed for a while, then keep it out for the same amount of time it was compressed. Do you have storage on a roof rack, or storage in a unit that attaches to a trailer hitch/proper trailer?