When I was searching for my truck, it didn't take me long to realize I needed a Dually. First, while my 310GK was 16k (+/-) I decided I wanted a truck capable of towing 20k plus. I wanted this extra capacity not only as a safety factor, but also as a "someday we might get a different camper" and need more truck factor. Second, it didn't take me long to figure out looking at the towing capacity tables that a Single Rear Wheel truck was going to be a bit light when it came to towing my 310GK.
And Last, the SRW trucks ride higher than the DRW trucks and both my wife and I liked that the Dually was lower and easier to get into (and it is not because we are short [I am 6'4" and my wife is 6'1"]), we just liked getting into the Dually better than the SRW.