The US Department of Transportation, as well as the Federal Highway Administration, address overweight in numerous laws. Mostly they are concerned with truckers (FMCSA), but not "all" the laws say "commercial". Therefore, they apply to all vehicles on the road. They can & Have pulled RV's across the scales and done safety inspections in Pennsylvania.
In fact, after a tree trimmer hauling a wood chipper killed a few people, the local creeper cops attacked anything towing...anything. The local construction guys sure found out that the backhoe behind their 1/2 ton wasn't legal.
At a minimum they can nap you for "Operating an unsafe motor vehicle". Got anything not tied down in the trailer? Unsafe--improperly secured load. Both would really put a bummer on what is hopefully a good trip.
I am not hear to argue the point. That is a dead horse on many forums.
