Basically, what you get in the cave kit, will make The Cave. But if you want to make a Cave that is completly closed, then you need 2 cave kits + the 1 wall piece from the Cave Bear. You need 7 wall pieces to go all the way around, as the 3 wall pieces that come with the cave don't quit reach the edges of the base. So, 6 wall pieces aren't enough to go all the way around 2 bases.
Actually, for me, that was a lot of the fun back when I first started re-collecting these kits. The thrill of the hunt. Yeah, it was a big bummer when I lost, but man, it felt so good when I scored something cheap!