I to do a lot of mountain driving and never had a problem with my Lance 815 and 2004 Dodge 3500 with single rear wheels. Only thing I added was the stable loads to engage the overload springs sooner. Think the trick is to not be near the capacity of the truck.
On my new 2015 Ram 3500 with single rear wheels, I have noticed more leaning but still not bad. However, I have not added the stable loads to this truck yet.
A rear anti-sway bar, such as hellwig, is also an option and will greatly help too.
One of the reasons we went with a hard side is we have access to 100% of the items 100% of the time. Granted it isn't hard or take very long to pop the top, but because I stop often, it would be a pain to do it. Much prefer the full height without popping.