If you saw my Toy Room Preview #1 you know I have several of the GI Joe play sets. I just picked up a Transportable Tactical Battle Platform (TBP) parts lot off ebay. It actually arrived today and I'm very happy with it. The base is nice and light gray. All the tabs seem to be in good condition. I will be using it to replace the badly yellowed base to the one in my collection.
As a kid, my friend Sean had the TBP, and I loved it. It's got a landing pad, computer center, giant gun station, missile launcher, and crane. You can also add string to the four hooks on it's base and have the GI Joe Tomahawk Helicopter pick it up and transport it.