I used to suffer from carb icing with my 1.3 ALL the time and was really really annoying
When i happened to mention it to an RAC man when we were chatting, he said you could get a heated temperature probe in the airbox, and this wouls stop it. I asked the garage, they said they hadnt heard of it, but the "official" VW recommended upgrade was to force the flap into the hot position with a screw or similar so that it only ever had warm air, and never cold. I did this (with the option of reversibility) and not once suffered from icing since. The car never ran too hot in traffic/summer either.
Same as said above, when the weather was really cold, it would rarely carb ice, it would do it on warm/cool mornings with the condensation/dew, and it would do it along the motorways, not when cold, but mostly in the summer etc.... v annoying, and glad to have fixed it with such a simple modification!