One of the most difficult challenges any employee faces is "managing the manager." It's hard to direct your boss's behavior even though you lack any authority to force him to perform a certain task. However, there are a couple of approaches that may help you.
As you plan for a show, determine when you most need your boss nearby. For example, is it when a certain client will visit? Is it during product launches, or when the press visits the booth? Once you narrow it down, meet with your boss to see if he will agree to be on site for those occasions. You could arrange to alert him via text or phone call, after which he would return to the booth, or you could try to schedule demos and appointments with clients and media at particular times.
If that's not feasible, see if your boss is open to meeting with clients or the media for coffee, perhaps, or lunch. (Some things, such as product launches, obviously, might be impractical outside the booth.) Ask if he'll agree to preset appointments on or near the trade show floor. If not, gauge whether he'll take meetings on the fly, with you arranging the rendezvous, again through text messages or phone calls. By using these simple approaches, you'll give your boss the latitude to roam, but be able to rein him in when and where you need him the most.