First thing that comes to mind is loading, is there anything heavy in the RR corner? Sounds like the RR corner has a 1/2" drop that is producing a corresponding rise in the RF corner. Maybe water tank is located there, at 8 lbs/ gal, a 50-gal fresh water tank then weighs 400 lbs.
I would also have a look at the right side suspension, spring hangers, equalizer, etc to be sure everything is bolted together right.
a 1/2" out-of-level by itself is not a huge deal as long as it's not a symptom of something more serious.