If you have a door from the DR to the horse area, you can clean out the horse area when you get where you're going and put a little porta-potty in the horse area for those nervous pees, at night or when you're in a rush. Check out the "Luggable Loo" at Amazon.com - trash bag and kitty litter and you're in business. Easy to dispose of!
I love my "Luggable Loo." My partner-in-crime and I refer to it as "Lou" and I visited him quite a bit last spring when we were at an event and it was snowing outside. She was somewhere without me and called and said, "I wish I had Lou with me." Who would have thought we'd appreciate a bucket with a seat so much?