Brian,
I just turn on my countertop water filter and hold the cigar at an angle underneath the stream, rotating it so all sides of the wrapper get dampened. Take special care not to let water get to the cut foot otherwise troubles with lighting will arise. If your tap water is good, then just use that. However, in my area, the chlorine is so heavy that boiled tap water is essentially undrinkable so I installed the filter.
Since I have been doing this, I have never experienced a cracked wrapper smoking outside in the cold. Plus, it makes the initial stages taste "meatier." And if you can keep a Cameroon wrapper from cracking in the winter, that's gotta be an effective strategy.
Wilkey