Thousand Trails is now part of Equity LifeStyle Properties.
We received a Thousand Trails membership for no initial charge when we bought our RV.
When we were full timing, we used TT a lot, especially in the Pacific Northwest which is one of our favorite areas.
We've had to cut back to RVing only about 6 months a year for various reasons, but we winter in Arizona in an ELS park, and the discount for being a TT member more than pays for the annual TT dues.
It can be a complicated decision, and individual circumstances can vary widely.