Fog of war system using masking

Hello guys,

I’m really new to the materials editor. I’ve been trying to create a fog of war system for my RTS. I’ve managed to do it with normal BSP and a dark material combined with another material that is masked and has opacity of 0. It works while in BSP, but once I turn it into a mesh it stops working and I can’t seem to be able to recreate the transpert effect. here is a screenshot of the BSP

Anyone knows why that is happening? I’ve added collision and it’s not working!