We camped at Iron Creek Lake after the rally, at the end of August.  It was wonderful, not crowded.  The cafe/diner has things like burgers and ice cream, and the fishing in the lake is great.  The trail around the lake is easy to walk and there is some beach area for frog catching and splashing around with little kids.  This is a great lake to have a water toy like a kayak, and there are rentals available too.  We have a 30' TT and didn't have any problem at the far end of the lake setting up flat and level camping.  Power was there as well.  There are many sites here on a hill, so depending on what you get, you may be in for a tricky parking situation with a longer trailer.  We didn't even use the dumpstation as the way it is positioned I couldn't get the tanks dumped, so that was a bummer.  We went into Spearfish campground owned by the city and dumped there.