Prepare for sticker shock:
http://www.wsdot.wa.gov/ferries/fares/ :E
It may behoove you to call them about your RV, with respect to the ferry you are looking to use. link:
http://www.wsdot.wa.gov/Ferries/infodesk/faq/general_info/trucks.htmReservations and deposits
Washington State Ferries provides reservations on two routes: Port Townsend/Coupeville and the international route to and from Sidney, British Columbia.
Reservations can be made online at http://www.wsdot.wa.gov/ferries/ or by calling 1-888-808-7977 at least two hours in advance of the desired sailing. Reservation deposit amounts will vary based on the length of the vehicle and the season (peak vs. nonpeak). The deposit amount is based on the senior driver/vehicle fare for the length of the vehicle. If a driver arrives with a vehicle that is a different length than the reserved space, the driver may be required to forfeit the reservation and travel on a space available basis. No reservation deposit refunds will be given at the tollbooth.
Anacortes/San Juan Islands/Sidney, B.C.
Reservations are recommended for international travel between Anacortes and Sidney, B.C. Reservations are required for international travel between Sidney and the San Juan Islands.
A deposit toward the cost of travel is taken for this route. The deposit amount will vary based on the length of the vehicle and season of travel. Deposits will apply toward the cost of travel. Travelers need to cancel a reservation at least 24 hours in advance of travel to receive a refund. Changes to a reservation must be made at least two hours in advance of the time of travel.
Fares collected in Sidney, B.C. are one-way to Anacortes but allow eastbound stop-offs in the San Juan Islands at no additional charge.
Commercial vehicles are prohibited from travel on this route. Half-fare promotions on this route apply to recreational vehicles and buses. Canadian currency is not accepted at U.S. ferry terminals.
Port Townsend/Coupeville
For travel before June 17, 2012, a deposit will not be charged for a reservation. A deposit will be charged for a reservation for travel after June 16, 2012. Deposit amounts vary, depending on the length of the vehicle and season of travel. Travelers must cancel a reservation at least 24 hours in advance of travel to receive a refund of their deposit. Reservations must be changed at least two hours in advance of travel. Weather and tidal conditions impact travel on this route. Please check our website before traveling.