The RV measurement that decides your ferry fare, and why your listing omits it
Washington State Ferries charges a vehicle under 30 feet roughly double if it stands over 7 feet 2 inches tall. On Anacortes to Friday Harbor that is $128.90 against $256.75 one way. Only 33 of 473 Seattle RV listings publish an exterior height, so ask the host before you book.
How this was worked out
WSF publishes separate fares for a vehicle under 30 ft under and over 7'2" tall on every route. Outdoorsy publishes an exterior height on 33 of 473 Seattle listings.
Divided the tall band by the short band on all seven routes measured, finding a multiplier between 1.96 and 1.99 every time, then counted how many listings publish the dimension that multiplier turns on.
What to do
Request exterior height in writing from the host before booking any ferry trip, and price the crossing from the band that height puts you in.
$255.70 round trip to Friday Harbor, decided by a number 93% of listings do not show.