Originally Posted by spock123
What does it cost to join and what kind of discount
Depends on the membership. But the most common one is their zone passes. For about $500, you get access to their parks in a specific region (they've split the country up into 5 "zones"). That gets you 30 nights of camping. Usually there aren't extra fees; but sometimes there is $3 extra for 50-amp service. Once you hit your allotted # of nights, any additional are $3/night.
You can stay up to 2 weeks at a single park and then have to be out of Thousand Trails entirely for a week. Some higher-level memberships allow 3 weeks and others allow you to go directly to another TT park.
There are a lot of memberships available for sale. As dblr said, if you use the system and want a national membership, it is best to buy a resale. Make sure to get the member number and call TT with it. They change contracts when it's sold and often times you lose some features.
And yes, as mentioned - almost all of the parks are first come, first served. You're guaranteed a place to stay, but not a specific site nor even full hookups or 50amp.