Definitely get reservations. Many places do close right around Columbus day (October 12 this year), and some earlier. Also be prepared for quite unpredictable weather; it may be warm and summery, or it may be cold and very occasionally even snowy.
I'm not sure quite what "ideal RV country" is, but there are plenty of people who manage to camp around here, and have a great time doing so. There are a handful of roads that one should avoid with an RV (for example, traversing Smuggler's Notch), but a whole lot of loveliness to be seen. It seems ideal enough around here for me...perhaps excepting the dead of winter.