We are in Chicago (DuSable Harbor) and cross the lake several times a year. We far prefer New Buffalo for all the reasons set forth by sailortjk1. It would be a great place to keep a boat (of course, having one 2 miles from home in Chicago is even better).
As you come into New Buffalo from the lake, and head towards the municipal marina (no turns), there is a set of condos on the right just before the municipal marina. You might try asking around up there, as they all have slips included, but not all the condo residents have boats. I have a friend who lives in these condos and I could ask on your behalf about availability of a slip for the year, as well as any regulations on whether this is even allowed.