We change little or nothing here between summer and winter shooting, all types of weather freezing to 100 degrees (we dont' shoot much at 100- except at Hefley and only for a few days - we hope.
We see no fouling changes from 6% humidity at Hefley Creek rondy or 40% here, to 95% when it's pouring - except the rain washes the fouing off the barrel and creates problems in the pan. I usually don't shoot in the rain, but do get caught on the trail now and then.