But heaters? I once compared the heat produced as driving by someone lighting a match on a street corner. We carried an ice scraper in the bug so we could scrape the ice off the inside of the windshield.
On my old bug I used bailing wire to wire the heater valves open every fall, and then every spring I would take a pair of dykes and cut the wire free to close them up again.
You ever notice how many old VW owners have a towel or a rag with them in the front seat to wipe all the condensation off the windshield? If you wait for the defroster to do it for you you'll be there all day.