D & K you are doing it right!
Going with a truck that will have "Room to spare" so to speak with the load you are carrying/towing. Going with the "Dually" is a decision you will not regret. I have owned both single and dual wheel trucks. The added stability with the "Dually" is something that cannot be shown in specifications.
Another aspect of tow rigs that comes into play is the old "Length and weight on a tow vehicle make more stable towing platform".
My "Little Red Truck" weighs in a hair over 9,000 pounds with a full load of fuel. (90 gallon aux. tank) Last time I scaled the rig in my sig. it came in at 23,000 pounds. Now that is with only abut 20 gallons of water in the 110 gallon fresh water tank, black and Grey tanks empty, loaded fairly light (On a trip by myself) and me OUT of the truck. (Truck was full of fuel)
I have pulled my Toyhauler with the F-350 "Normal" dually "Shop truck". (Almost a carbon copy of Ken's truck) There is a noticeable difference in the seat of my pants between how the two trucks towing the same trailer. The only differences are, "Little Red" weighs almost 1,000 pounds more and has a 6" longer wheelbase.
I'm looking forward to seeing some posts of how the combo you are putting together work out.
Catch Ya Later,