I didn't read the whole thread. In my area there are county and city campgrounds that they could get in. Finding small out of the way places would probably work best for them.
They will have to lay kinda low though. By that I mean that if they attract attention to themselves by being loud or anything else the cops are going to show up and shake them down. If they are quiet and keep to themselves mostly then they would have no problems in the small public campgrounds in may area or even state parks. They might have a problem finding spots though. Especially at state parks.
If they decide to come through SW MN (like on I-90) send me a PM and I can point them to some nice spots where they will have no problems.