There are several things you can do. No. 1 is insure him if you can! ;D I don't know how far out from show you are and what he is weighing, but I would keep feeding him and getting him fat. If you have to cut back on anything, cut back on the feed and make up the volume in grass hay. (Make sure your hay is grass and doesn't have any alfalfa in it). Since you said you haven't tubed him yet, I take it that he is just one of those that blows up and then goes down. I personally think putting them in cool barns adds to the problem because they don't get as much excercise. Walking them or just getting them moving helps with digestion - just like in humans. Add the baking soda to the feed and some probios wouldn't hurt either. Finally, when you are a couple days from show, put him on pretty much hay only. He should stay slim and trim for the big day.