Could you have the bad flex run replaced and while the contractor is there have him check the main? You could just have an isolated area due to the bad DIY fan install. If the area of contamination is isolated to the one run then you may be in luck. If the whole supply is contaminated you have months to find a good contractor to solve the problem WITH you.
Does anyone else in your area have an AC only system like yours? May ask contractors in area if they do this and what they do to prevent the condensation in the winter.
If you could add strips to your AH you could run it enough to keep the condensation out?