Brett, 60 days is indeed the length of time you can stay in the State of Washington without a permit and without paying sales or use tax if you can prove residency in another state, but to be legal on the 61st day, you must purchase a permit. At the time of purchase we were given the option of 1-90 day permit, or paying for two 90 day permits for a total of 180 days. The advantage of doing this over a 1 year cruising permit (I was calling it a cruising permit, because that's what it had on the form when we paid, it may have another name as well) is that you can leave for a period of time (not sure how long), then come back and start the process over again with purchase of 90 day permits.
I don't know the relevant RCW, I'm not an attorney, and don't feel inclined to pay one to find out the RCW behind it, but those were the options given to us by the State of Washington on purchase. The State Officials who collected our money may have been in error, but I'm betting they weren't.
If you wish further clarification, I suggest you retain an attorney to research it for you!
On the other hand, feel free to ignore what I posted! It was worth everything you paid for it!
Just trying to clarify the issue from our recent, personal experience.
As always, it pays to be informed, but the bottom line is to get out and USE YOUR BOAT!
Fair Winds and Following Seas