I've hunted in the Big Horns above Sheridan in Region C. The locals there have told me that getting access to private land can be real tough. But there are lots of roads in the National Forest that are decently maintained so there's really no need to worry about security. I found the locals to be pretty friendly and helpful as well.
That said, because of the access issue, I much prefered hunting Region R on the west side of the Big Horns. In addition to the National Forest, Region R has plenty of BLM land as well. Moreover, I saw far more mulies and elk in Region R than I did in Region C. There are cabins for rent in that area so you might consider going that route as well. Better yet, book yourself a motel room in Ten Sleep, hunt from dawn 'til dusk, and then sleep in a warm bed at night.
Just my two cents. Good luck on your hunting trip.
