my daughters ambo ,and son's van and caravan have been parked on our grass for years . the ambo goes out for odd weekends , the others are just for major festivals.the wheels have sunk about 1-2 inches, if i was worried about it i'd put the bottom of a bread tray under each wheel . the grass under the vans usually recovers after a few months , wheels have quite a small footprint , paving slabs will kill a much bigger area
we also put a 4 metre pool on the grass for the whole summer, which kills the grass ,but quite a lot of it comes back in the winter