We bought our "new to us" 2008 RV last September from a local WA resident. She had bought it used almost a year earlier from a dealer in Arizona. She said the dealer told her to just put the plate from her trade-in (WA plate) on the newer RV which she did. She drove that way for almost a year until that plate expired. Then she sold the rig to me. She never paid WA sales tax on her purchase even though the RV spent most of the time here in WA. When I went to register the RV I took the Arizona title, in her name, signed over to me, paid the sales tax on our purchase and had the new plates and WA title issued to me in my name. Some people have more guts than I do. I'd never drive around in a vehicle that has plates registered to a different vehicle. But I sleep pretty good at night.