No matter what you use - make sure the first time you use it is NOT at an actual event. ANYTHING for distance riding should be broke in prior to a ride. Would be a potential disaster to find out 15 miles from camp that your horse or you are reacting to something!
Don't worry, I totally know this! I have been a runner for a number of years and I'm sure trying out new tack at an event would be equivalent to trying out new shoes in a marathon!
I think I've narrowed down my search to either mohair or a prof. Choice neoprene. I may just try to pick up one of each off ebay
and then resell whichever one I don't like as much. I really appreciate everyone's advice.