Idaho does have smog, but only for vehicles newer than 1981. It does NOT, however, have a safety inspection like Texas or PA, where you get an inspection sticker on your windshield.
I’ve traveled across the US numerous times in RVs or towing horse trailers without ever being stopped to be inspected by anyone, state or federal. One of the first times I ever towed a living quarters horse trailer, I stopped at a weigh station in Indiana and the DOT man told me they don’t care about vehicles with a less than 26,000lbs GVWR. Unless you are using your RV for commercial purposes, or it’s registered to a company, or it weighs 26,001lbs, there is ZERO reason for it to be subjected to a CVI.
Regarding smog/safety laws, vehicles only need to conform to the law that was in effect the year they were built, which is why I’m not required to have doors or a three-point seat belt in my Jeep.
