I stayed in Vegas for a week and a half last spring. Some of the places I stayed:
The truck stop at Blue Diamond Rd and I-15. I parked in the gravel lot next to the NOAA office. If you can tolerate background noise from the interstate this is not a bad place to stay. Lots of trash though, and possibly drug deals and other shady business going on at night.
The park and ride on Gilespie Street in Enterprise. As long as you have a basic measure of stealth you can stay here overnight. $20 will get you a three day pass for the buses that go all over the city from the terminal, great if you want to do some drinking on the town. Not very quiet but a safe location.
Railroad Pass Casino outside Henderson. I believe they are covered by a Henderson town ordinance that bans overnighting in RVs, so if you don't have a stealthy rig this isn't the place ot be. The highway noise subsides at night.
Hoover Dam Lodge/Casino past Boulder City. Trucks use the lot so it gets noisy. Quite a distance from Vegas, though.
Kingman Wash campsites. Exit two on Route 93 on the Arizona side and a few miles down the gravel road. The receding lake has uncovered a quarter mile of new road so there are plenty of campsites to choose from. Scenic setting, quiet as well.
Boulder City bike path parking lot, Veterans Drive near the Cascata Golf Course. Only distant highway noise.
Curb camping in North Las Vegas. A sketchy neighborhood by any measure, but north of 515 there are many streets that can be camped on. Downtown is a short walk away.
Curb camping west of I-15. Some other RVs curb camp in the industrial areas.
It is technically illegal to camp in the BLM land immediately adjacent to the city but some of the hills near Blue Diamond Road are kick-ass places to camp, with the view of the city and all. 4x4 required.
Probably best to make a big loop, spend a few days in the city, then go camping in Boulder City, then out in the desert, then back into Vegas again. In my experience, Vegas police aren't concerned with van campers passing through, but probably wouldn't like long-term parking in any public area.
Thanks again!