The answer to question depends on several things related to what you are going to do with the rv and your residency. Are you buying new or used? From a dealer or private party? What about titleing it in your home province?
You are going to have to have a title for it from somewhere, but not necessarily register it. That is likely when you will get taxed, if not done in Oregon.
I live in Washington and purchased my current trailer from a dealer in California and had it delivered to my house. The dealer gave me the option to pay CA sales tax on the purchase. I declined, because Washington tax on it would be higher and I would have had to pay the difference to WA upon titling it. My thought for doing this was I don't live in CA so if I am going to pay the same total in taxes why do I want to give that money to a state I don't live in. Something else I discovered when deciding how to get it to my house. Was that if I towed it home and spent the night in it while still in CA I technically would have been required to pay the tax to CA.
Since it sounds like you are planning to park it long term after it is in CA. I would be inclined to title it in OR and use trip permits to get to the final destination.
Most insurance companies will cover new vehicle purchases for a couple of days without being notified.