This is again, comparing to California law, but likely it will be very similar in other states.
You can register any pickup, including dually as an RV (or non-commercial) vehicle when you have camper on it.
I went for inspection with my TC to change the registration, but on daily basis I have camper shell. Having open bed might cost me hefty ticket, but the trick is saving me at least $300 a year on registration weight fee.
Icing on the cake, I can drive with camper shell and legally tow my 18,000 lb equipment hauler while ignoring scales.
