If it were me, I'd be staying at Great Lakes Marina. Good slips, a ramp right next door, Crazyhorse keeps his boat there, as does Fred, and usually Jafo. I'm thinking I might stay there that weekend too. Unfortuanately, I don't have their number, but they are listed with Information. 231-555-1212 would be the number you need to call to get it.
Redstripe, gofastboater, or Crazyhorse would probably have the number handy though.