Yes, I got the Canadian travel permit because the previous owner did not want to leave his plates on the trailer. (I don't blame him).
I was able to get the Idaho permit in advance because I live in a rural county (and had all the info on the trailer), and the county clerk had recently gone through the process about 1 month before with someone else, just before I made my inquiry.
Who knows what Washington requires!
Contrary to the earlier post, yes, there would have been duty on the Surfside
if it had been a much later model. However, I wouldn't worry about that. It's not that much $$!
You will still have to pay Washington Sales Tax (I suppose) when you register it there! I did in Idaho!