For us, the biggest headache as full timers was initial warranty work on our new rig. If you are traveling all over you probably will not be close to your "selling dealer" when a repair is needed that first year or two. At least with Keystone Montana dealers it was like pulling teeth to get them to honor our factory warranty in a timely manner since we didn't purchase the unit from them. For that reason we wouldn't be trading very often as full timers.
But the main reason we would stay in a unit for up to 10 years before trading would be modifications and maintenance. Once you get the bugs worked out of a new fiver and get all the options installed you need/want it is time to sit back and enjoy. I really don't think it is much different than owning a sticknbrick in that respect, you probably wouldn't switch houses every 2 or 3 years.