Thousand Trails have been around for a long long time...because of the way the ORIGINAL business was run, unfortunately there are probably as many 'plans' out there as Carter has liver pills. The very high pressure salesmen could 'adjust' their basic plans to fit the customer, within reason of course. Therefore many plans are unique. Since you said you're going to buy used, which is by far, the best choice, you'll have to call TT with the membership number and the owner's name. They will tell you what is included in that particular membership. Ours, bought used, includes all TT parks nationwide, along with most NACO and Leisure Time resorts. That said, we discovered there are a few LT resorts that are not included in our membership. They were added later and were not grandfathered in. Most TT memberships allow you to go from park to park with no out time, IF you only stay 4 nights at each campground. Ours lets us camp for two weeks and out one week. All memberships can be 'upgraded' from basic to premier to gold to platinum to elite....all come with substantial cash outlays, so beware.
Finally, some offer fixed dues if you reach a certain age but not all do. TT can raise most dues 10%/yr, so it can be substantial over time. Also, some memberships DO NOT allow you to cancel. Make sure any membership you purchase allows you to cancel with a 30 day written notice. There are many more campgrounds on the west coast than there are on the east coast. There are very few in the heartland.
Not all cgs are exciting. Equity Lifestyles, (parent company) is a little tight with the purse strings so a lot of the TT cgs struggle to do upgrades etc. Also, TT has started offering long term stays, (one year or more) some for as little as $2000/yr. You can judge for yourself what quality of 'resident' they get for $165/mo. To add salt to the wound, many of the 'best' sites are offered to long term tenants. So, with this in mind, my advice would be this:
TT memberships are available for little or nothing on Craigslist, Ebay and others. BEFORE purchasing, you'll want to get the membership number and owner's name and call TT to know what you're buying. I would buy the basic membership as cheaply as possible...there will be a transfer fee of course and the dues must be current before the membership can be transferred. By buying the basic membership, you can try it out with very little cash outlay. If you like it, you can either upgrade or sell it and buy the one you want.....good luck....Dennis