I think you might want to check with your insurance company regarding insurance coverage. Since your truck MAY not be properly registered...will the insurance company consider it to be unregistered if you have an accident or other insurable loss??? Don't just check with your agent...check with other agents/insurance companies and the DOT/RMV. The money you may be saving may be peanuts compared to what you may lose.
I believe that motorhomes have their own category of registration...I think it's "Auto Home".