There have been at least two rallies in MT and one in CO. Most rallies happen closer to the person that wants to step up and organize it. It is a logistical nightmare trying to set one up far from home where you might have never been before (hence the reason you want a rally there). NATCOA has not had many volunteers to set one up farther away. This past year, the rally was in eastern OR, very close to Northwood Mfg's factory.
I have attended a truck camper rally in MN hosted by Doug in the midwest and they now have two or three scheduled events per year with a good following.
The east coast also a good group of people that seem to mostly be from the northeast (excluding people like Gus and Stu) . I have met a few of them out west or in the midwest, but have not had chance to make it all the way due to a full time working schedule. We will be making a cross country trip in April this coming year to NC and are hoping to make the gathering in Apex sponsored by D&H RV.