Sniffer:

Time to find a new mechanic IMO.

The build up of condensate is problem 1. It is prevented by using the vehicle as it was designed, ie drive it long enough. If that isn't possible then you need to clean it out when the condensate collects. You could also clean the CCV annually.

Collected condensate freezing is a result of problem one. Call it problem 2. You should put your efforts into solving 1, dealing with the root cause, not just focusing on the consequential symptoms. Dealing just with insulation and heat tracing is like putting a piece of black tape over a dashboard warning light. You can't see it anymore, but it is still there and the problem it is indicating is still there. Even if it doesn't freeze, the collection of moisture is a warning sign relating to short trips, accumulated moisture, and resultant accelerated wear.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue