cowl rust problems.

My 66 Dart has severe rust problems around where the heater box and vent holes are. When I removed the vent box from the drivers side the whole pan came with it. All the way to the bracket for the parking brake. The passenger side is only a little better. My question is if I am not going to use the heater could I weld in a patch over the air intake area in the cowl to stop the water? I tried to patch the pan but have had no sucess.