Trying to think of places. If you go out to north western Indiana, you could take a train into Chicago and check that out for a spell. Indiana Dunes NP is supposed to be nice but no hookups, if I recall. I have family in the area and found a couple of campgrounds.
Otherwise, I'm a fan of the New Jersey shores if you haven't been. I think you mentioned you might have been.
Not Disney, but Orlando has Universal. I think Universal is soooo much better than Disney for teens. But, that's right at your 900 mile mark.
My kids are a bit younger than yours, I think.
