Going AZ there are hills no matter what way you travel from Oregon. You might have to invest in a set of chains, just in case of snow, and the road sign indicates that chains are needed. BIG fine if caught without them.
The last time we came back from up there, we took I-5 almost all the way down through California, and some how wound our way to I-10 into AZ. Look for LARGE truck stops, Casinos, But pay attention to signage that limits camping in any out of the way place. If in a Wal Mart, do not make it look like that you are camping, You are just resting for a few Hrs if asked.