my experience was i had rain gear on the whole time. got north of alliance and put rain gear on. got to rapid city and stopped at kmart to buy hand/toe warmers. had 2 in each glove and boot. got to stugis and i had to have been hypodermic. instead of camping in tent. i got a small cabin with a hot shower. warmed up. went for a ride around sturgis, went to deadwood and down spearfish canyon. that was awesome even in the rain. got back took another hot shower. watched the news. weatherman said in the morning it will be 47. by noon it will be 42. i checked weather on my phone for buffalo, wy. high was gonna be 35. so next morning i packed up and went home. when i went through keystone there was a sign saying 42 degrees. i think after mount rushmoore it was even colder.
i did carry the whole time. never did see a sign anywhere. i think Sd signs dont have any legal weight behind them.
not sure on reservations.