We were returning to Tucson from northern California a couple years ago in late September and had the same idea.... good luck. :S The forecast called for highs in the upper 80's but by the time we reached Panamint Springs {mid morning}, it was 104 and 107 at Furnace Creek.
Saw 230 degrees of trans fluid and 224 of coolant on the climb out of Panamint in our 24' Class C {2012 V-10 towing my motorcycle - bike and trailer were less than 1,000#}. Both cooled back down after the top of the grade and we were able to maintain 45 mph but it was NOT much fun.
:E
Chances are good that you will encounter triple digit temps and the climb out of Panamint Springs is monstrous. Once you get over that grade the rest of the ride and subsequent grades are no problem and Pahrump is usually a lot of fun, we like the Lakeside Casino RV Park {formerly Horrible Herb's}, though expect temps in the 90's.
:C