Originally Posted by CanoeStream
I've always followed this advice. Parking longterm on concrete will pull oil out of your tire bodies and leave dark marks on the floor. I don't do this during my multiple back-and-forths in the summer but I do roll the tires onto 6 mil poly for the longer winter storage.
It's not the concrete that pulls oil out of the tire bodies. It's simple gravity. A smooth, light-colored concrete surface just makes it easier to notice where the oil has come out because the oil soaks into the concrete and leaves a stain. Parking long-term on ANY surface, with the tires not rolling for long periods of time, does the same thing. If you left the trailer parked long enough for black spots to form under the tires on concrete, black spots would form on the poly sheets, too, except that the oil washes off the poly sheets when it rains.
Most people don't let their RVs sit long enough for oil to leach out of the tires onto the pavement, unless they end up accidentally or deliberately turning their RV into a lawn ornament.