I realize this is an older post but I have some info on a decent campground near the twin cities metro since I live nearby.
Lebanon Hills is a county park extremely close to the Minnesota Zoo. One campground has water, sewer, electric sites, while another has electric only, and length restrictions. Although located in a populated area near the metro it does not feel that way in the park. They take online reservations, and, although fairly busy... generally are not full to capacity in the summer. You should be able to get in there with most any big rig. Link:
http://www.co.dakota.mn.us/LeisureRe...Campground.htm
I've also camped at many Minnesota state parks and have visited 72 out of the 75. If you have any questions on the state parks... Just ask.