New RV's depreciate like crazy, and will drop in value during the first few years... so for that reason, I echo the "buy used" sentiment. I bought our 2008 bunkhouse trailer in 2015, and it is/was in great shape. And I got a GREAT deal on it. New RV warranties aren't worth a whole lot honestly, and if you DID need warranty service the trailer would be towed off to the dealership and you wouldn't be able to use it for days/weeks while parts were ordered. That wouldn't work too well since it would be your primary living space.
Gary mentioned quality fit & finish issues with travel trailers... I love ours for weekend/vacation use, but not many of them are designed for full time living. Many (if not most) fifth wheels will be more heavy duty in that regard. Better insulation, cabinets, furniture, flooring, etc. I know you said you don't want a 5'er (did you say why, since you'll rarely be moving it anyway?), but just something to consider.
Bunkhouse trailers are going to seem really cramped, really quick, unless you are in the 30+ size range. You'll realize this once you start looking at rigs in person. Imagine a rainy week, and being stuck in there for several days on end with each other.
Most important factors for buying a used RV are budget, floorplan, and condition. You'll notice year/make/model aren't on that list! Check out our "Library" link near the top of the page, for all kinds of articles on RV learning & living, including inspection checklists to print out and take along while shopping/buying.
The longer you take to make this decision, the better chance you'll make the RIGHT decision (for you and your circumstances). Research, take your time, shop constantly (online and in-person when possible), and keep asking questions!