We once stayed at a sleepy place right on the south edge of Deadwood. I was nothing fancy but nice, unfortunately do not recall the name.
Have you considered taking I90? It is a little shorter drive, and maybe stop near North Platte. There is a Cabella's parking lot in Sydney. That you most likely can overnight in for free.+
Edit: Just looked up the Sydney Cabella's. They even have electric sites for RVs. Not free, but looks convenient.
https://stores.cabelas.com/us/ne/sid...ela-drive.html
https://www.google.com/maps/place/Ca...4d-102.9569446
Another edit; That Cabela's might be a longer drive than what you want ~9.5 hours, but there is a time zone change in there somewhere. There is another in Kearney NE, that might be closer to the 1/2 way point