When we had our 22,000 lb gas motorhome towing a Honda CRV we had no problems as long as we took it slow going down. Now we have a 33,000 lb diesel motorhome towing the same CRV and we love our engine brake.
Of course we were from the West where we have lots of mountains. I have seen many, many older motorhomes taking these same mountains all the time. The old rule of thumb is to go down at the same speed as you go up the same hill, which works if the slope is the same on both sides. Mostly the slope is not the same on both sides, but you get a feel for it. The other rule of thumb is to go slow enough so you can slow 5 to 10mph at a time with the brakes and not have to do it often. That might mean 20mph. You don't ride the brakes, you put them on and slow 5 to 10mph and then release.