Thank you for all the feedback. This has been quite an education. I seem to go thru it every few years when we change units so I tend to forget the details.
We are keeping the Solitude 378 unless someone can recommend a similar quality floorplan with smaller GVWR and hitch weight. Love to hear about alternatives.
Regarding the truck, I returned my beautiful King Ranch F350 today. It felt bad but it was the right thing to do.
I have come to accept that if you want a large 5th wheel, you need the dually. It will be dedicated to towing mostly and we will use something else as a daily driver. That may help keep the resale value up.
We are not fulltimers even though we will spend most of the summer away from the Arizona heat.
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...
Thank you again.
MC