Long shot, anyone used WA state as home base?

Jfet wrote:

Would the physical street address of something like that place in Aberdeen be usable and legal as a home address? I would hate to get in a $100,000 auto accident and have my claim denied because I used an improper address for my RV insurance.

Call insurance companies. Tell them that you have an RV and that you want to live in it full time and use a private mailbox as your domicile as you don't have friends or family who will let you use their home address for your domicile. Ask them what they require in a policy to do this.

I went through 4 insurances companies before I found one that would work with me. Much of what I posted in that link came from them. They told me about the street address. They told me that "PMB" doesn't work with the DOL and to list it as an apartment number. I asked why. They said that even they run audits against their own policy holders and PMB might generate a phone call from them about my policy. On their advice the address on my policy reads like an apartment address.

I'm not going to handhold you through the process. Don't fixate on the private mailbox so much. WA doesn't care in the least if a PMB is your domicile. Find an insurance company that will work with you and give you everything you need for what you want to do, at a cost that is acceptable to you. It's doable. Just put in the sweat equity.