In Wa state, ballots are mailed out. You fill it out put it in the mail or any of a number of ballot boxes you will find at Grocery stores malls outside of post offices. If you have an address you vote. They should try that for caucuses.
Mail in voting is wonderful. Here in TX, we have mail in ballots, but only for people who might have a harder time voting (e.g. older adults and individuals with disabilities). Would love to see this expanded to all voters.