Cliffside is a nice park but has the disadvantage, which it shares with state parks, of having no full hookups. Staying "a week or so" means you'll be having to leave the campsite to dump periodically (unless your MH has huge waste tanks!) :)
That said, state parks in the area are a good option, though some may be booked solid on weekends, as reservations open 11 months in advance for Wisconsin parks. Some nice parks we have enjoyed that are within 50 miles of MKE: Kohler-Andrae SP near Sheboygan, Point Beach State Forest outside of Two Rivers (also a good base for Door County), and Richard Bong SRA west of Kenosha; there's also Harrington Beach SP between Sheboygan & Milwaukee. All of these except Bong are right along Lake Michigan (so is Cliffside, which is a county park). Any of them - with the dump situation noted - would make a good base camp for Milwaukee as well as other things to do in southeast Wisconsin.