I’ve used Swantown Marina in Olympia for cruising in the south sound. We parked truck and trailer for 10 days with no issues. Parking truck and trailer connected was $10/day.
For middle sound cruising, we used Everett Marina Launch area parking at $8/day last year. Not sure if there’s a limit on the max number of days though.
Anacortes offers trailer and truck parking at several lots at Cap Sante Marina. Not sure of a max time limit for the $5/day trailer parking but truck parking is free and seems not to have a time limit. Cap Sante does not have a launch ramp though. The travel lift to get you in/out of the water is about $80 round trip.
Our main launch is at Bellingham’s Squalicum Marina. You get 5 days (truck & trailer connected) launch area parking included with your $9 launch fee. They don’t like you staying past 5 days but you could come back every 5 days, pay another launch fee and extend your cruise that way.
We take our boat up from Ashland once in the spring and park it in between cruises at a farm off Cook Road in Burlington. Keri, the manager, charges about $70/month for a 30 ft trailer with or without boat on it. During cruises, we launch at Squalicum, move the trailer 30 miles to Keri’s farm, drive the truck back to Squalicum and park the truck free in Squalicum’s general area parking lots. No issues in past 7 years of doing this even though some cruises are over 3 weeks long.
PM me if you want Keri’s contact info.
PS: I highly recommend getting some cruising guides for your trip. We use Waggoner’s and Dreamspeaker Guides.