Oregon used to be a great state to "Live" in with a RV. But recently (well in 2006 when I registered my RV here) the prices went way up. There was a charge for the RV length, to be paid one time the first time that the RV is registered in Oregon. So if the RV was owned by a prior owner in Oregon, it only has to be paid once. Mine was not, so I had to pay something like $20 per foot (31' or $620? Maybe it was only $10 per foot). Anyway you also pay about $100 per 2 years.
Washington State used to be really expensive, but a bunch of them got together, and decided who runs the state, us or them. They passed a constitutional amendment to limit registration fees to only $65 per year, unless the VOTERS decided to raise it. So that might be a state worth looking into.
I have heard from some members of the Escapees club, and they have their mail forwarded to their "Home Base" in Livingston Texas. However they also need to bring the RV back to Texas every two years for inspection, and have to renew their drivers license near their birthday in Texas as well. That can be a pain if you are wanting to spend the rest of the summer in Alaska, and then realize that your tags expire in August, while you are 5,000 miles away! And you need to have a Texas company inspect the brakes, frame, emissions, ect.
I don't think that Washington requires frame and brake inspections like some eastern states. Nevada is also a great state worth looking at. There are many companies that will serve as your mail forwarding company, and you can put your drivers license address there. I don't think they have income tax, but might have sales tax. Oregon and I thing one other state do not have sales tax. Something to consider if you will be replacing a $300,000 motorhome.
BTW Back when California registration fees where very unreasonable, my buddy bought a $275,000 COuntry Coach. His first year fee was 2% of the purchase price, and the additional fees that all vehicle owners pay, like $65 more, and some other tiny fees like $2 for call boxes along the freeways. Total was something like $5,700 for the year.
DOn't complain to loud, it is not the most expensive place to register.
Fred.