Cave rule question

[TheBigRedOne]

I believe your interpretation of the cave rules are correct.

As for sealing them, you are right, it is out of the scope of the game, and would probably require more explosives than an individual in SB would carry. I doubt a satchel charge is powerful enough to seal the opening of a cave, especially a larger sized one. In many cases in the Pacific the US would seal them using bull-dozers after eliminating the initial threat with flame-throwers or explosives.