I've just remembered today after me n the woofie got soaked how much fun it is trying to keep an old car ie Boris with his 1959 heater demisted !!!
Hence previous owner supplied Terry the towel free !!!
i use rain x anti fog or use shaving gel smeer gel onto the inside of the front window then wipe of and the the window wont mist up https://www.youtube.com/watch?v=8Vj9avZxuwI
Provided that the demister pipes are fitted correctly then the fug stirrer heater should be capable of keeping the windscreen clear with only the driver on board. Any passengers should be instructed to stop breathing and given the yellow duster and told to keep wiping. Alternatively you could try opening the quarter lights but that risks your fingers from suffering from severe frost bite