If my dog gets upset, he has seizures. With the 4th ....?

of July coming, and he does get upset when he hears something like gunshots, how can I keep him calm enough to prevent it. Was thinking about trying to go camping but have two other dogs and the oldest one isn't up to such an excursion, and there are idiots everywhere with loud fireworks. (Needless to say I can't go watch them being shot off because people around my place will be shooting them off too...not the pretty ones, just the loud ones.)