It's so mild this year that it's causing havoc for horses with coats.
Re the mane being rubbed by neck covers... My solution so far has been - mane and tail spray on both mane and neck of rug, neck cover has to be kept fairly clean, and not to get a build up of grease, if it needs washing, you can either just scrub it with a brush and water or chuck it in the washing machine with correct detergent (especially if it's a detachable neck). Also I never pull or thin the mane from autumn until the spring when they stop wearing a neck cover, just used scissors to shorten. This means that if you do lose any mane then you've still got plenty left and also I found that as soon as I thinned it for some reason the whole lot just went.
NF with PPID is fully clipped in a 50g wug (so no neck), but will move up to a 100g with a neck if it gets cold. Hes is funny, gets shivery if wet (which is poss the PPID) although he doesn't mind his neck getting wet. I tried wintering him with a full coat the first year I had him, but he sweated so much when ridded, I gave up clipped him. Recently discovered he has PPID so we are seeing how he goes with a full clip as his coat was coming through so thick and was curling along his back. He is sweating loads in walk despite the clip, which is bizarre as in the summer heat, he barely sweated at all when I rode him. He does run hot unless he gets wet, when he becomes grumpy and shivery. Our PBA has an Irish clip and 100g rug with no neck unless its pouring. She early 20's and cant keep herself warm if she gets wet.