Look up Oak harbor beach park. the city has a full hookup RV park by the beach. It is clean and handy to stores and shopping, such as it is on Whidbey. Walking distance to the downtown shops & restaurants.
I don't know the cost but there should be space unless there is a big event in town. Some people stay for extended periods but it is definitely intended for short stays.
Deception Pass State park does have some electrical/water sites. if the campground map shows a tent, it may be big enough for your Escape
but will not have services.
i agree that as far as i know, the campgrounds around Coupeville and the south end do not have hookups.
Let me know if i can get any more info for you.