So sorry for your mare!
My horse is out for only 3-5 hours in these conditions... So from my perspective they are brilliant. I dry them everynight, but neoprene dries quickly.
i've used some other in the past (can't remember brand) and they were a nightmare. They were folding up easily (this...
I'm fighting mud fever now as well. Now I'm using equi chaps for turnout, and when he comes in I towel dry them (i've clipped the pastern to make everything easier) and put Fucidin (from vet) on the bad places and MSM Equiminis cream all over the pastern. In the morning I use sudocream instead...
http://www.equilibriumproducts.com/leg_protection/equi_chapsreg_close_contact_chaps/
How about this one? They are neoprane, but breathable. My horse is not out all the time, but I use them and his legs are ok. And they're good to prevent mud fever!!