How can I fill a specific zone?

Hello everyone, I’ve been working a few months on UE4 so I want for the game I’m doing to fill it with a destructible mesh in a specific zone because in that zone will be placed some actors in realtime and the player has to place it wherever s/he pleases and then other player has to attack that destructible mesh to find that actors. It also has to be possible to save it for a second attack, so I would like to ask you which options do I have to do it possible? I’ve been looking for creating a geometry brush then turn it into a destructible mesh but I don’t know how in C++

Thanks you for your attention

PS: The game is more like Fallout Shelter