Many mountain grades can be uncomfortable no matter what you're driving, especially curvy ones where you may have to suddenly stop because of an accident or similar incident, but you shouldn't be fearful of them.
A well maintained RV, towing a vehicle at or below it's weight limits, should be able to traverse any mountain grade. It's all about appropriate speed and use of your brakes if necessary.
Remember, back in the 50's, 60' and 70's, a station wagon with drum brakes was often the family vehicle of choice for towing those old trailers. I'm guessing back then, many of the large grades in the US were in worse condition (narrow and windy) then they are now.
It's all about common sense and as Clint Eastwood would say, "knowing your limitations".