Okay after driving a truck for many years I can tell you a little about DOT regs. First of all these are DOT Federal laws underneath the state laws. If you weigh 10,001 or more total combined weight, you are considered a commercial vehicle by Fed law, and you must cross the scales. This includes roll backs, and wreckers, of course I have never seen many have issues by not doing so. Busses and RV's are exempt because under law a RV is considered a bus. A pull behind camper is considered a commercial vehicle if it puts your CGW over 10,000lbs. If you are pulling an empty trailer rated for 12,000lbs you are required to have a class A. It doesnt have to be loaded just registered for that weight. Or a truck registered to tow more than 10,000lbs the same rule applies. It has been known for a long time that the DMV enforcement is a source of revenue for the states, and they can many times ignore you, or fine you several thousand dollars if they feel like it. That being said if a trooper, or dmv asks you to cross the scales or be weighed on the roadside no matter what you are driving, they have the authority to do so. Just remember all other laws apply to this as well. If you are towing your rig, and your combination is above 10,000lbs (yeah that would be everyone) you also must log your hours, and have a DOT health card if you travel more than a 150 mile radius from your home. Sounds impossible, but yes its true. Will they ever get you on this probably no, but they have laws to fine you with something if they feel the should. Remember it's a crime to pee on a pine tree in NC punishable by jail time!