AZ to WA avoiding steep hills

I don't have an answer but I would suggest that if you want to do mountains with an RV and are uncomfortable with hills you might want to reconsider. As long as your tow vehicle is rated to tow the load you have, hills are just a matter of slowing down and downshifting on down grades. Shouldn't be really scary. If it is, then you have the wrong set-up or have a sort of hill phobia and might want to quit. You didn't specify your tow vehicle. Super important to make sure it's hefty enough with both power and braking; possibly heavier duty than a half-ton pick-up. Assuming you stick to main routes not back roads.