If you feel adventurous get off I-15 at the Nipton exit and go thru the Mojave Reserve. The route is pretty well signed now; two right turns head you to Cima (old Boxcar post office), on to Kelso (historic train depot/hotel) where a left turn heads you to the I-40 crossing and down to US-66. Another right turn runs you through Amboy (a ghost town trying to come back). After that the first left turn puts you on the road to 29 Palms (RV park there). Then, go west on CA-62 till it hooks up with I-10.
The road is not perfect (some is rough, some is whoop-ti-dos, some parts are out of cell coverage) but it will definitely keep you alert, and there is not much traffic. I've driven it several times in a Southwind, and have met quite a few RVs (DPs and 5th wheels) while doing it.
Balfre, we have taken this route several times going to and from Palm Springs to Las Vegas through Kelso stopping at their lunch counter for lunch (great chili hot dog). There are no dirt roads, all paved and no problem with our 42 ft. coach w/toad. Beautiful scenery!
If you haven't seen Roy's gas station in Amboy, it's a true step back in time.
And, if you do decide to make the Yermo stop and it's around lunch time, you have to go across the freeway and have lunch at Peggy Sue's 50's diner. It's a busy place with good parking and good food.
2015 Prevost Liberty Coach Elegant Lady, 45 ft, 4 slides, 500 hp Volvo w/def (incoming Nov. 2014)
2008 Monaco Dynasty, 42.2 ft., 4 slides, 425 hp clean-air Cummins diesel
2013 Honda CR-V EXL, AWD, w/Nav, SMI Air Force One vacuum-assisted braking