I know someone posted a similar request several days ago and got several responses, including some thumbs up for Cliffside. We stayed there once (albeit with a smaller unit than you have). Pleasant little CG, electric & water sites, no sewer. I don't remember if there was a dump station. There isn't much right around Milwaukee itself.
How far away from MKE can you be? Bong SRA west of Kenosha/Racine is nice, and a few sites will fit a rig that long. You can reserve up to 11 months in advance (and I'd recommend it.) Electric hookups only; dump station available.