I would hesitate before hanging anything - even soft foam - against the side of the caravan. Over time, the continual slight movement (from the wind) will wear marks on the thin paint coating (dirt/grit will get into the foam whatever you do).
I would consider using two (or three, depends on body length) 2' fence panels. Stand them in a line beside the van, screw a batten along the top and the bottom on "your" side, then attach three battens at right angles from this base, one to go under the front steady, one under the rear one, and one under the wheel. Attach a diagonal (use ordinary door hinges) from each of these battens up to (near) the top of the fence panel (another door hinge). You need to set it up away from the van to get the measurements right first. (How close to the van do you want it to stand?) To use, jack van up, slide whole thing into place, lower jack, lower steadies - the barrier is now rigidly supported at a distance of x" from the van. (OK, put some foam along the top edge for "just in case", but unless someone really crashes into it you'll be fine. You could even make a "door" partway along to give access to the van door, but that's a bit over the top!
If you don't want some 2"x2" under your tyre, fix the batten to a bit of board and use that under the tyre.
If you're handy with a saw and screwdriver, the whole thing need cost no more than £50 using B&Q