I have done some checking and as far as the info I can get is that a truck that was licensed as a commercial vehicle previously can in fact be switched to a RV tag as long as the truck is used as an RV. And this makes sense to me since the new owner of my 81 W900 Kenworth bought it for just that purpose. As far as state to state I'm not sure. But here in Ky a big rig can be switched to an RV tag with an inspection by the fire marshal.