Inupait (eskimos) aim to NEVER SWEAT. Reduce your workload or clothing to be a bit on the cool side so your own sweat isn't adding to the problem.
And, since polypro and fleece became widely available 30 years ago, we have the option of WEARING CLOTHES THAT DRY AS YOU WEAR THEM.
Couple those concepts with shedding rain while having good ventilation (poncho, embrella, tarp, etc) and trips in constant rain get more comfortable.