Generation One cartoon continuity
Moonbase Two was the second Moon base built after the Decepticons' conquest of Cybertron. It appeared to be smaller and less extenstive than Moonbase One. Spike Witwicky and Bumblebee were stationed on it. Like Moonbase One, it existed just long enough for Unicron to come along and eat it. Unlike Moonbase One, it actually got to violently explode in a (feeble) attempt by Bumblebee and Spike to destroy Unicron.
According to the Official Ladybird book Adaptation of Transformers the movie ( which came with an Audio cassette), Moonbase 2's main Function was as a Forward Observation Point, and store house for a vast quantity of the Explosives and weaponry the Autobots had been stockpiling in preparations for the attempt to reclaim Cybertron.