I'm thinking of purchasing a Columbus 385bhs GVW 15940. But I'm unsure if a new 3500 Dodge Longhorn mega cab SRW with a tow capacity of 16720 will be fine for towing, or should I move to a dually. ...
I'm in the minority. If the numbers do not exceed the truck, I'd get the SRW. But as said earlier, check those numbers for your payload. That was the only reason we went from the an SRW to a dually: the pin weight was way over.
As for stability, I never thought it was a big difference. I went from an '09 F350 SRW to a 2011 F450. Stability with both trucks was absolutely fine for our 44' toy hauler and driving an SRW as a daily driver is much easier than a dually. IMO.