Hy,
I have a dually r17 and tried the 19.5 single . just bad compared to the dually. the camper center of gravity is high and on uneven pavement roads when the camper leans on one side trust me I want a larger rear base. + dually has a lot of traction, barely needed the 4x4 even on Colorado mountain roads roads. All this BS with the stone stick between the dually is nonsense,, just look between the duallys before taken the highway. And air down I down air down , I drive more slowly when roads are bad.As for sand if it' s soft you'll get stuck anyway. Also on highway speeds a flat on the dually you don't even feel it. At 75 mph had a flat and all I felt is that my truck didn't want to advance any more. I thought I had an engine problem not a tire problem. And again at highway speeds I don't worry too much if turns are tight because I know the 2 tires sticking outside provides more than enough lateral stability....
The only time singles will probably do better is in the mud when going forth and back you create tracking( just got stuck in mud with my dually because the outer tires were pushing too much mud and I don't run agressive offroad tires .I got out with the winch. BUt I,m Not convinced that singles would have done better since the terrain was really soft Probably I would have done better with singles and agressive mud tires .
4 tires are better than 2 in the back where is the load.
this is my personal opinion based on my experience others and took the singles route and they look happy. So different built different needs.
as for the shocks I would buy the Bilsteins but put 2 each side. These are heavy rigs and mine when it swings from side to side in potholes one shock is not enough to control the load.( or the leafs)
hope this helps
incognito