Some of the Casinos have outside parking - Back of Ballys/Paris, Excalibur etc and folks have stealth camped there for a few nights on and off for years. Things have changed past couple years though, with automatic arms for access and changing for parking at most of the Casinos on the strip now. Something to bear in mind if you are entering and exiting a lot of Casinos for entertainment now!
In many years gone by we have liked the Oasis but as has been mentioned got way too pricey, although you can get Passport America rates at certain times so check into that. If you are needing to be Strip/Freemont area dominant for a short stay and can sleep well, then maybe Main Street Station or Circus Circus (latter was shut down but reopened when redevelopment plans got shelved!). We stayed at Sams Town area May 2017 = LV RV Resort, Nellis Blvd once and probably wouldn't again unless you have your own transport. Felt very sketchy walking around there especially at night, and the shuttle contract is up I believe this year, and with the new bid we were told that Sams Town are not opening it up to non patrons! Hearsay but don't rely on the shuttle without checking out the facts. Cabs from Sams Town to the Strip are pretty costly and regular bus service quite time consuming.
Just some food for thought to look into a little further depending on your individual needs.