Hello - We had planned an inaugural trip with our Minuet to LV this past March, but ended up at Zion NP in Utah instead (stayed at a wonderful resort there which is about 1 1/2-2 hrs from LV and which I wrote up in the Campsite Forum), but I did get some recommendations on some places around LV. One of them was this one:
which is on Lake Mead right outside of LV. Probibly would be pretty nice in Sept. and maybe not so crowded. I believe there is a Wally World real close too. Once you click on the above and connect to the link, go down the left side to "Lake Mojave" under Cottonwood Cove, pictures. That will link you to pictures of the RV park and info itself.
By the way, many of the people camping at the resort close to Zion NP were fulltimers wintering there. It was really nice. Good luck. Leigh