I personally don't like the vaccine either, but i'd much rather have my horse have a sore neck for a day vs. getting strangles. We had a major outbreak at the barn i'm at before I got there, and my friends horse had it and she said it was horrible, and she almost died.
I don't know what you've read, but they do a nasal or a shot. I would recommend giving the shot at least a week or two before the camp. If your worried about reactions I give my horse two grams of bute the night before and the day of shots. I also think it helps he is in the pasture. He has horrible reactions to his shots, and I did the bute for the first time this year, and he is the only horse that was fine.