If you are going to use the boat in CA then having your residence in OR won't make any difference. If you would actually be using the boat in OR, then it might make some sense to establish your residence there.
Besides sales tax you also have to consider property taxes. Not sure about CA or OR in this regard, but a number of states will charge you a percentage of the value of the boat each year as a personal property tax. North Carolina
does this (or at least did, when I lived there).
But the real answer is, a forum like this is not the place to get tax advice. Seek out a professional, or find the answers yourself on official government
websites. Tax advice from a bunch of strangers on an internet
forum like this one is worth exactly what you pay for it--NOTHING! At best, someone might be able to point you to the proper government
websites to find your answer.