It can be useful for "mod-makers", so I reveal how I create caves for the new Viet War Pack. This trick should be available only for scenario designers or during battles against human player...
I create a first cave unit (any APC class, but with a speed of "0") and a carry capacity of 255. Then a second cave unit with a weight of 10, 20, 30... (what you want). During the deployment, I load the "little cave" in the "big cave", sometimes with some one/two men infantry units named "Booby traps" (speed of "0") and armed with... Booby traps, mines, bombs, etc...
When the first cave (big cave) is destroyed, you have the other one (little cave) in the same hex, like a kind of tunnel network... It runs for VWP, but also in Afghanistan, during Pacific War, in Stalingrad, Warsaw (sewer network instead of cave...).
So, you have formations called "Caves" or "Tunnel Network" with two caves (or 1 cave/1 tunnel, etc), and booby traps devices...
Best regards,
Laurent Touchard