As to how often I trade, which takes us back to 1988 when my sons were 4 & 8 and we bought our first pop-up:
Starcraft Meteor - bought used. Used for one year to "test the waters". Wife & kids loved it. Following year, traded in for Starcraft Flyer (10' box).
Starcraft Flyer - liked the trailer but after two years, the roof failed. Starcraft was going to replace the roof under warranty, but we decided to trade it in for a Starstream (12 foot box).
Starcraft Starstream - great trailer! We kept it for 10 years. Then, we bought a 2003 Sunline 29' trailer.
Sunline trailer - what a great trailer. We kept it for ten years. With our move to a 55+ community in Ohio, we had to get a smaller truck. So the Sunline was traded in for our Winnebago Minnie which could be towed with our Tundra.
Winnebago Minnie - purchased in the fall of 2013. So, we are now starting our fourth year of traveling with this trailer. With our truck being a 2007, and we're up in our sixties, we're contemplating making a change in a few years. Our gargage is awfully tight with a Tundra and a Subaru Outback. We're contemplating moving to a class C or smaller class A motorhome and pull a smaller car behind. It would be nice to have something with auto levelers, and perhaps a little more room than our Minnie. But...we'll have to see. My wife and I really enjoy travelling and exploring new places and we've discussed many times that with advancing age, we'll just have to make changes and adapt as necessary.