Skeins..You'll need to get your boat and trailer inspected by State Patrol. All out of stated vehicles to be licensed or registered in Wa have to go though this. Then you get to pay sales tax and possibly an exise tax and a registration fee. Fun fun fun. At least the sales tax is 1 time only. Contact your county auditor's office and they can tell you how much the grand total is going to be. Sounds scary, but the sales tax is going to be the biggest expense.
It could be worse, you could be licensing all your cars too. Ooops, maybe you are.