according to
http://www.dol.wa.gov/vehicleregistration/moving.html
"If your vehicle is a motor home, RV, or trailer, you MAY be required to present proof of sales tax. If you do not have proof you paid sale tax when you purchased your vehicle, you will be required to pay use tax."
IIRC... there is a limit as to how many vehicles you can bring in to the state without having to pay use tax. I brought 2 cars, a utility trailer and 2 motorcycles, and I believe they required my to pay use tax on the MC's even tho I had proof of paying sales tax at time of purchase.
The WA DOL and DOR web sites are very good, otherwise there is a listing of phone contacts for licensing offices, I recommend this one 360-397-2288 (Clark County office) They seem to have greatly improved their 'customer service', tho there are still a couple of 'grouches'.
