You average car tire wears out before the UV can do them in. It also helps that the flexing while driving moves the oils to the surface.
The end result is your average car tire is worn out in 3-4 years long before UV damage can take out the side walls.
RV's often sit for months at a time. It's not unusual for a tire to be 6-8yrs old with only a few thousand miles on it and full tread depth. So failure method is aging out which is heavily impacted by UV damage. If you can stop the UV damage, you can increase the life.
I wouldn't bother if only stopping for a night or two but if it's going to be in storage for a month or more, certainly makes sense.