I do think she was on 40 and that's how she got back into AZ (probably unaware) when she made the VM to Travis, and IIRC in her testimony she told JM she stopped in Buckeye Lake for gas on her way to Travis' - she didn't need gas there as she had 3 full cans in the trunk from Pasadena. Granted she might have paid cash and not saved a receipt as it would prove she was in AZ but I doubt it, could be where the Buckeye Lake came from though. As far as I know she didn't stop for gas that night until she hit Mesquite, NV, but I also don't think she went over Hoover Dam, she'd have been stopped for the upside down license plate, I feel sure.
This is the route I was thinking she had taken, as for disposing of evidence, between rest areas, truck stops, wide open spaces etc it wouldn't have been difficult. Heck, she could have stopped at any one of a number of campsites anywhere along any of the routes and made a wee bonfire, she even had extra water to put it out with when she was done.

I dug this link up again, does it match up with what we know?
http://www.hlntv.com/slideshow/2013/02/11/jodi-arias-trial-tragic-roadtrip
"
At 5:33 p.m. There is a picture of blood on the baseboard.
<snipped>
At 10:30 p.m., Arias calls Burns to tell him she got lost but she's on her way and will be in Utah by the morning.
In the 11 p.m. hour, Arias calls Alexander's phone three times:
The first call is at 11:37 p.m. and is 31 seconds long.
The second call is at 11:48 p.m. and she leaves a voicemail.
The third call was at 11:53 p.m. It was 16 minutes long.
Investigators say Arias may have accessed Alexander's voicemail account on June 4. Phone records show Arias was
between Kingman, Arizona, and the Nevada border when she made the calls.
JUNE 5, 2008:
West Jordan, Utah
Between 10 a.m. and 11 a.m, Burns says Arias arrived in West Jordan,"
edit note: just for reference, it took her around 12 hours to get to RB after calling him approximately 45 miles from Kingman... it takes 6 hours from LV, 8 hours from Desert Hills, either would work with her claim of having taken another nap, which she told RB, or plenty of time to stop and clean up any evidence, gas permitting.