RE: Rapid City SD
Hey Hollis!
We've only been FT in the summers here (near Rapid) for two years so my info is based on what I see and have heard from the locals ... we arrive in June and leave with the geese mid-September. The previous seven summers have been dry and warm/hot (depending on your perspective) on the northern prairie while his year, provided a wet and therefore green look to the prairie. In July and August you can expect a few days to be above 100 degrees at the hotest (none this summer however) though the heat is dry heat, not like back "home" down South. Evenings are pleasant and progressively cooler as you get into September just as they are in early June.
Wind (we call it breeze) can come off the prairie at any time and can be quite strong at times. You need to be aware and not leave your awning unattended. The "breeze" during the Sturgis Rally (25 miles west & north of Rapid) this year, had me helping replace several awnings and related gear whilst costing the less-than-careful RV renter four figures or so.
All in all, the area of Rapid City is a good summer location, my favorite thus far. Plenty to do and see in the near-by and good eats and friendly people all round. RV camps, sites and parks are all over the place and all over the price ranges ... you'll find much to enjoy.
PM or post if you have specific questions .. I'll try to answer.