Being turned out 24/7 is a great start for treating ulcers.
I bought my horse ~4 months ago, and have suspected that he has ulcers. He seems better since I got him, but is still sensitive in the flank and last week went off his "grain" for a few days
(And he also cribs, but I suspect he's been doing it so long that he will never stop completely)
The first thing I did was put him on a grain-free diet. He came in a bit underweight, so I fed him rice bran along with his ration balancer until he got to a good weight. Now he just gets his ration balancer and supplements. Because there was the possibility of ulcers, I put him on U-gard and ProBios. I also give him aloe vera juice whenever I'm there at feeding time. He also gets alfalfa cubes in his Amazing Graze stall toy. I'm not planning on continuing either the U-gard or ProBios when I run out, though.
A friend at the barn who has done a lot of research for her own horse recommended the supplement Succeed
. It's fairly pricey, but is supposed to alleviate hindgut ulcers as well as gastric ulcers. I've ordered a "taste test" for my horse, and if he'll eat it I will probably try it for at least a month.