Here is where you can check.
Weigh Stations | AAA/CAA Digest of Motor Laws
Some say commercial vehicles, some say passenger or specialty vehicles (RV's) over 10,000gvw towing a trailer (toad) must stop. There doesn't seem to be an consistency between states. Some states bring everyone in for a safety inspection, in that case they check everything including the skid marks in your shorts.
I think for the most part they really aren't after RV's for weight although some could use a safety inspection, especially for tires and brakes. They do watch for suspicious RV's that may be transporting drugs.