Will agree with some of your statements, only because it is impossible to carry more weight and NOT reduce fuel economy and payload capacity. But in the 350/450 I have used the tank in, any mileage decrease was negligible (60 gal = 420lbs) and payload is not a problem running solo, and in the 450, I am still ok loaded. As to moisture, I have never had the WIF light come on--and I change filters at 40-50k miles--sometimes much longer. It is not a storage tank, as it HAS to be used when it has fuel in it due to gravity feed. I run it empty about 50% of the time unless I notice a real good bargain in price. No one that I know of who has one of these tanks has had a moisture problem--aluminum doesn't rust/corrode in presence of diesel. If it were a steel tank, that could be a problem.
It is extremely helpful to start a long trip with enough fuel to preplan where to take on more, and when towing my 17K trailer, 38 gallons wouldn't last long enough to suit me. Then while set up in a CG, much easier to take on fuel without the trailer.
I have had the tank for over 90000 miles driving, and have saved enough to pay for the tank cost.
'05 36TK3 Mobile Suites
'10 F450 new to me
'09 F450 Lariat 4x4--died