If you aren't looking for anything too fancy you could try
State Fair Park in West Allis. It's really just a parking lot with hookups.
A better option is
Cliffside County Park in Calendonia, which is just south of Milwaukee county. It's not very far from where Pug Fest is held, and only 20-30 minutes from most things in Milwaukee. It's a beautiful little park with 95 sites, most of which are very large, some with water. Lots of big rigs there all the time. No sewer though.
See the Harley Museum. A bit pricey but well worth it, especially if you like history and engineering/technology. See the Milwaukee Art Museum. One of kind unique building, free to enter and see the Calatrava addition. A fee to visit the entire museum. We also have a beautiful lake front and beach area which is just north of the art museum.