Dave, many campgrounds also rent trailers or cabins on site. They also have unpublished rates that they will negotiate for groups. A lot depends upon timing. Tom F has experience with this type of thing.
For example:
http://www.bransonstagecoachrv.com/rates.html
I am not suggesting we go there. It is just an example of the business.
I think we would find similar facilities in many other places; worth looking around.
Bob