"I have ordered the same King Ranch with a dually from the same dealer. Price is just about the same plus or minus $1000. I get a 48g tank, an 8 ft bed, no need for helper springs, room to carry a bit more w/o worry, room for a cargo box, an extra pair of tires in case of a tire issue and peace of mind.
Worse case, we keep it for a season. Best case, we love both the truck and 5th wheel as much as dually owners here seem to like theirs..."
FWIW, which is about $0.02, I believe you made the right choice. I no longer RV, but for a few years, we pulled a 38' 5th wheel with an F350 crew-cab, long bed dually in KR (years ago). We had to carefully pick camping spots sometimes (i.e. older state parks don't like 60' or so of combined setup), but we really enjoyed the room of the big truck and trailer....and we always made a point of using the truck to see the local sights: it didn't take long before we were both relatively comfortable driving the truck, although it didn't replace the Prius as our commuter vehicle.