Buzzy4 -- Good conclusion there! I own a 2004 Nissan Titan, a model that I believe pushed Ford into the inflated "Towing Capacity" claims as they introduced their new F-150. 9000 pounds -- WOW! At the time I had a 4000# empty weight Argosy. As you can see I am also heading for a 25' Safari. My decision on the Titan is looking a bit anemic. These 5.4L engines (Ford's & Nissan's) are great and have all that power. But a half-ton is a half-ton is a half-ton....
A stable tow requires tongue weight to be 10-15% of the overall trailer weight. Figure closer to 15%. Also look at http://www.airstream.com/product_lin...aq.html#weight
It is critical to look at the tow vehicle's GVWR (Gross Vehicle Weight Restriction) -- as it stands alone! Now the Titan's "Vehicle Load Weight Capacity" (Useful Load) is as high as 1641# in the simplest form, and my 4WD King Cab's is only 1367#, while a 4WD Titan Club Cab's is as low as 1202#. At the F-150's website
I see that Ford's 4X4 Club Cab has a "maximum payload" of 1530#. That vehicle has a 30 gallon tank I see -- okay, 189#. Your various options weigh: (fill in the blank). A truck cap weighs: (fill in the blank). You and your partner are a charitable 350#. By the way, did you actually put anything in the bed of the truck? All of a sudden the maximum tongue weight must be under 700# and your gross trailer weight must be something under 5000#.
So, yes, I definitely am loading light after I get my new trailer. Once I settle into the finances of that purchase I am looking at a 3/4-tonner for sure (gotta love those Power-Strokes, though the Allison trannys start a whole 'nother argument). But you are ahead of the game because you didn't upgrade from your 2003 to a 2006 F-150. The GVWR for an F-250 is still somewhat finite -- an F-350 will carry anything but the suspension is mighty hard on an Airstream belle! Congrats on a well considered decision!!