Thanks - back in the real world now! Sounds like we were a bit east of where you're thinking of - were at Wells State Park, right on Lake Michigan. Surprisingly the lake wasn't frozen this year - just a short distance out. Last year the boys were able to walk as far out as they could and still couldn't see any unfrozen areas. And the gas station we were at when I typed my last reply had all the Yooper merchandise you could want!
Just one bit of advice I'd have for your son. You will take the CFA at both NASS and WP SLS. They will (or can) both count towards your actual applications. My son went to NASS first, and although he had practiced some at home, of course it was kind of new and overwhelming to him. So he did well, but not quite as well as he would have liked. He was determined to do better the next week at WP, but they were MUCH more stringent about what qualified a correct pushup, etc. there (ie he did had about 20 not counted since they weren't "correct"), plus just having sore muscles from the last week and not as much sleep as he would have liked meant he did much worse overall. I'd definitely have your son be psyched and ready for the first one he takes before he gets tired, especially if it's at Navy.
I do think a lot of how "intense" it is depends on the cadre. My son had an awesome squad leader at Navy. They never had any down time and he was always working with them or having them do some kind of activity. His WP SL didn't seem to want much to do with the candidates, and any time the schedule allowed for "squad time", just sent them back to their rooms to hang out. Although my son appreciated the down time (after a hectic week already), he found that seminar to be much more boring and thought it lasted too long.
Incidentally, we did consider doing the same thing as you last year. Doing the two East Coast ones back to back, but decided he'd rather fly home and sleep in his own bed (and since we weren't going with him, the logistics and transportation issues made the prices about the same) for a night. He wasn't nearly as tired after each one as I'd been expecting, but cumulatively it was definitely exhausting. I think the main complaint was simply the lack of sleep - they usually didn't go to bed until around 11 or later and were up at 5ish and were active all day. He'd looked at a sample NASS schedule before he went and was very "ooh, that looks tough, a whole hour of PT, ooh, and then intramurals too!
", but had a very different attitude when he got back. Many of his texts from that week said simply "I'm SO tired". However, he said the PT at any of them as a whole was very easy but of course they used lots of different muscles and think everyone was sore/tired by the end no matter what!
I do think it there's any way you can juggle these that it's definitely worth letting them get this experience to know what's right for them. If you haven't, check out youtube for some videos of some of the activities or the summary DVD/videos from some of the summer seminar programs which may help get a feel for what they'll be doing. Until we watched these, my son was kind of debating between doing two or three. After watching them, I kind of felt like he should skip one and take a week to recover, but he was completely psyched by them and felt he didn't want to miss anything and try each of them!
Good luck!