Vintage Air Question

[lts70]

I am installing a sure-fit system in my truck with a universal coil that will allow me to shave my fire wall and run a 4-way bulkhead for my lines. I found a couple trucks on the board that I really like and would like to do the same thing. These trucks have the bulkhead running through the original blower motor location. To do this I need to cut through the inner cowl vent area, I will attach an aproximate location. I will also attach pictures of the trucks that inspired me And my newly shaved fire wall.

Does anyone know if I need to do anything special to go this route? Like to prevent water from leaking from the cowl. Any advice on how to do this modification the right way would be greatly appreciated. Thanks Guys.