If you have a backup plan (i.e. MIL), I'd go ahead and let him stay with her. No plan is "ideal" for working parents on these days, including the camps. We do the camps on every day off and they do tend to get old; however, we don't have another (affordable) backup. If we did, I'd use it.
Also, I wouldn't worry about him being out of school for 5 straight days. The camps aren't academic either.