Have done it a number of times and will be doing it again in a couple of weeks. Waay more interesting and less stressful than trying to get around Seattle on the 405 or through on the I-5. Port Townsend is such a lovely town that I never get tired of visiting. The 101 down towards Olympia is slower and has more twists and turns but is very scenic and low stress. If you've never done it, gotta do it at least once. A 21' TT is a piece of cake on this route including the ferry.
The ferry fare is in incremental lengths. It's a good idea to know exactly how long you are overall in case the ticket guy makes a mistake. There is a method to how they load the ferry and may not be in the order vehicles got on the lot.
Taking the Port Townsend ferry is especially good if you want to head over to the coast like to Ocean Shores and from there down to the Oregon Coast via 101. Another route might be hwy 3 & 16 through Bremerton but that puts you in Tacoma and the Tacoma to Olympia stretch has pretty bad traffic too.
There are a number of CGs along that stretch of 101 if you want to overnight. There is a really nice small one of around 20 sites right on the Hood Canal waterfront. Can't remember the name or where it is, but it is a Good Sam and the old power generating station is across the street. One of the nicest we've ever stayed at anywhere. The trailer in the background in the photo is ours at this CG. Even if you don't need to overnight, it's worth a visit.
🙂Last year I went through Seattle on the I-5 and ended up with damage to the truck due to the miles and miles of constant rush hour stop-start traffic (should've left home earlier) and weight of the TT. Legally you are supposed to be in the right hand lane if towing a trailer, but that's so hard on the truck and trailer... Never again. 405 around Seattle is pretty busy and there's no good time of day it seems. Traffic got a LOT worse after Bill Gates moved to town. :m