Here in Canada the
Registrar of Imported Vehicles handles the
importation of US vehicles into Canada ... I would think the US government would run a similar department that handles importation of Canadian registered vehicles into the US. I know some US RV dealers near the border have complete details on the process of Canadians buying a US trailer from them and importing into Canada ... have you spoken to either of these Canadian dealers to ask whether they can similarly offer advice on importing a Canadian registered RV into the US?