Re: 1979 Chevrolet Bus
I'm not sure what it's called but I used a thin rubber with a sticky backing. I purchased it on a 4" wide roll at the Home Depot. I know it's used in conjunction with Tyvek and siding and all that jazz. I cut a 4" square, put it over each hole and haven't looked back. Putting silicone in the hole first might not be a bad idea for that added peace of mind.
Love the bus, I too fell in love with the body style and have to have it.
Passes everything but gas stations.