best thing is to not let em get rained on to begin with... I wrapped the seat in an army poncho as soon as I saw a cloud in OK, but **** DOES happen-
wrap the whole seat in a black lawn n leaf trash bag, seal the bottom up as best you can, cut a hole by the headrest and run a blowdryer into the bag near the bottom somewhere so the air vents out the top hole.
It's macgyver as all heck, but it dried my seat in about an hour. just gotta seal up the bottom fairly well, I stuffed towels under the seat
or you could move down to the mojave... haven't had a wet seat issue since I moved down from oklahoma in JAN