I've flown my model 4 without wing tank drains for 11 years with no problems but will add that I live in the desert where condensing moisture is much less likely. I always sump the lowest drain on my system which is the bottom of the aluminum header tank.

My problem comes now when traveling cross country into higher moisture content areas of the country where water in fuel can be a higher possibility. Without wing tank sumps, it takes about 10 to 15 minutes for water to reach the header tank if water is introduced to the wing tanks through fueling. I refuel first then go get a soda or restroom break then come back and check for water in the fuel.

My worst instance of water in the fuel in 11 years was at Cavanaugh Bay, Idaho after a night of rain and the next morning it was heavy dew and some fog. I drained close to 10 sumps of water out of the header tank before getting a clear reading.

I think I'd put the flush mount wing sumps in if doing it over. You could check immediately after fueling to see if water was introduced.