We stayed three nights at the Circus Circus KOA RV park, in one of the deluxe sites. It was a pretty good place. We had our own grassy knoll with an olive tree providing shade, and a table and chairs. It was a little pricey for an RV park, but it was good for us since Vegas was merely a stop on a bigger road trip and we had an infant and dog with us.
*pros*
they allow dogs
they have a really nice dog park
nice pool, with shade
nice hot tub
clean
safe
easy to find
clean bathrooms/showers
*cons*
pricey
takes 25 minutes of walking through casino to get to strip