I live in Sedona and have family in the San Fernando Valley (near Northridge). I've driven I-40 many many times over there and back, a few times with various motorhomes, all gas, some with tow car. So you should have no problem driving the route with your DP.
Needles is the hottest place! I stay about 20 miles east of Barstow at Newberry Mountain RV Park in Newberry Springs. Just a decent easy pull through for the night where I don't have to unhook my car.
From Barstow I either drive 58 to 14 all the way down to I-5 into the Valley, or I-15 down to Victorville then 18/138 over to 14. On 138 watch for left turn onto Pearblossom Hwy (to 14), else you'll end up in Palmdale.
2002 Itasca Suncruiser 32V
2012 Suzuki Grand Vitara