We drove from St.Louis to Yellowstone a year ago september and passed thru everything in South Dakota. Keep in mind that most of the tourist attractions (besides the monuments) are closed during the winter. The roads are scenic there but I wouldn't attempt them in bad weather and especially not with a trailer attached. I don't know when they stop getting snow there but it was surprising to my husband and I that there were gates on the highway to close it down in snow - in St.Louis you don't see that! We didn't find much to see between rushmore and St. Louis though - we did St. Louis to Sioux Falls, SD, then Sioux Falls to Rapid City (where rushmore is). If you decide to stop and spend the night in St. Louis, PM me and I'll make sure you stay in a decent part of town - much of St. Louis along the highways is kinda sketchy.
