LOL, Duffy, I'm your exact opposite. I'm so claustrophobic that riding in an indoor seriously freaks me out. I never knew it until I moved to OK, in CA & AZ we rode either in outdoor or max a covered arena, and you could still see everything around. The first time I rode in an indoor warm up at a show I FLIPPED! It's been 7 years and I've pretty much quit showing under saddle, I hate riding indoors so much. Take me out on a 25 miler or in a nice big outdoor, I'm fine. Oh, I'm sure the fact that my practice arena in my back yard was twice the size of these indoor warm ups has a lot to do with it, but still, it was a shock to find out how badly riding indoors in a tiny arena un-nerves me.
Only thing I can suggest is to get in a group of 5 or 6 riders and put Duffy right nose to tail with a real patient horse who won't be upset if you ride right there for security. Go for a very short ride, say around the outdoor arena once, just to start and then sit down and think about the positives of the ride. Then do it again either later that day or in a day or 2, and keep on doing it until it's not so scary to be in an outdoor ring. Then ride around the oustide of the ring, so on and so on, until you've expanded your area and time and aren't coming unglued by the outdoors. There's really nothing like the feeling of riding across the desert in the moonlight on a warm summer night! But folks who are timid about trail riding will never experience that. It's worth trying to work on.