Provided the camper stays connected to the truck, there really is no difference between riding in a truck camper, or riding in a class A, B+, B, or C motorhome, or fancy van conversion, without properly secured forward-facing seats with headrests and properly secured seat belts.
I agree that riding a bicycle, motorcycle, scooter, atv, skateboard or rollerskates/rollerblades, are all more dangerous than riding in a truck camper.
It really baffles me that AZ has a mandatory seatbelt law, but no mandatory motorcycle/atv helmet law. A simple 'fender bender' on a motorcycle can often result in death, whereas in a car there is rarely any injury at all, even without a seatbelt.
Obviously, government mandated 'safety' statutes make very little sense....