I don't know where you are speaking of in S. Dakota, but here is one place I 
know of: Mountain Meadow Resort # 605-574-2636.  There are covered tie-stalls, 
and full hook-ups for campers, a bathhouse too. Don't know the price, but if I 
remember it is reasonable.
Also, my favorite in NW Nebraska (in Crawford) is Ft. Robinson. $6.00 a night 
for stalls, and full hookups or cabins. This was the largest cavalry re-mount 
station in the US, and it is really pretty, with alot of history. 
#308-665-2900.
Hope this helps,
Kathleen