Ron,
The only way to be completely covered to to take out a workmans comp policy in every state that you will be working in. This I find is stupid. If you have a valid comp policy in WA and all the appropriate liability ins's you should be OK. "Caveat Emptor"
I travel around the country timber framing and raising frames and have asked this question many times. A valid comp policy number usually works for the contractor and will cover your employees. If you hire any CA labor they will not be covered by your WA policy.
The liscencing and permiting aspect should be handled by the general contractor homeowner or whom ever is running the show.
Hope this helps.
Good Luck
