my cab has the same problem im going to sand blast the outside to bare metal then put a thin layer of fiberglas over the whole front area and leave the weather striping out the vent will be covered so it will be gone thenn i will blast under the dash to remove most rust and paint with a rust sealing paint when a cab gets this bad its called the kiss of death but fixed this way it will last 10 or 15 years by then ill find a better cab or be tiered of the truck only other fix is a defferent cab