Check into Castle Rock and Petenwell Flowage in Wisconsin. We didn't catch a ton of numbers the time I was there, but we did catch some nice crappie. Both places have plenty of fishable area to spread out, and access was pretty easy. I'm thinking they were around the 5-6 hour mark or so from northern Indiana. I would also consider Lake Winnebago if I was going, although I have never been there. I think you could expect more walleye in there.