My buddy tows a huge fifth wheel with his 2010 F150 and the Ecoboost power plant. He is very pleased with 11 or so mpg while towing and 22mpg around town when not towing!
hmm. Payload, payload payload.
I agree with you Dan. Too much for a 1/2 ton. This is exactly what the problem is. People shop considering the towing capacity only.
Switz, you are doing what you have to do, plan it out. Mojo is right 1100 lbs. tongue WD hitch. Your homework is correct. I believe you are spot on with the 25' and would also be fine with 27' or even 28'. I believe that beyond that you may be getting to the edge- Payload and, as you say GVWR. You will have the power though for sure.