I live near Portland and I think your decision is a good one. There is no sales tax in Oregon and registration is very reasonable. There are also many places to camp here so you can make sure all the bugs are worked out of your trailer before you hit the road. You can get the information for that at State of Oregon: Oregon DMV
It is rather difficult to find a 2500 Suburban around here if you are in a hurry. I recommend, if you can, finding a trailer that you could pull with a 1500 Suburban, or get a 4 door pickup truck, they are very common and there are always many for sale.
craigslist: portland, OR classifieds for jobs, apartments, personals, for sale, services, community, and events
is a good place to look.
Registration is good for 2 years here, and every 2 years you need to have the vehicle emissions tested to be able to register. This is transferable so if you get one with valid license plate tabs you just have to pay the title transfer fee. You must have liability insurance.
I have had a good relationship with Curtis Trailers (a large local dealer) http://curtistrailers.com/