Gemma,
I have the info on Cameroon in front of me now. Essentially there are no known limestone caves, and potential is slim for any discoveries. However, there are a few lava tubes (up to 450m long), some labyrinth caves in block boulders and tectonic fissures, and a small stream cave formed in Laterite. It looks as if exploration is incomplete (a couple of French and Spanish expeditions).
The longest known cave is Grotte de Gaskin, a 450m long lava tube on Mount Cameroon. The next longest is the Goufrre de Mbilibekon, which is a 220m long stream cave in laterite. So it does look as if it will be worth your while taking some kit.
If you want details such as entrance locations PM me.
Cheers,
Ed