Yes, we have friends that do exactly that. You have to do a lot of research to get the plan that will work for you. I think most require a break of a week before you can go back into the Thousand Trails system. Somehow our friends' plan allows them to go straight into another park without taking the break. They bought a used plan from a broker and have added to it over the years so they have membership plans in other RV parks such as Resorts of Distinction.
We haven't considered buying into Thousand Trails for several reasons - crowded parks, large areas of the country without parks, and the necessity to make reservations in advance. It also doesn't fit the way we like to camp and travel.