Geez, I feel like I'm a little late here, but having worked at an airline checking bags at MIA for 20+ years I've got to put my 2-cents in.

Having had two Tiogas (for my wife and I), I do see your affection for them. We had to put one to sleep after our airline destroyed it on a trip to Calgary (and Jasper NP) years ago. What can possibly happen that could break one of the aluminum tubes on the frame?

This being a lightweight hiking forum, I do have a suggestion, and that is: If someone says this:

I'm pretty sure a boat or car cover shop in your town could make one [a duffel] rather easily (and fairly cheaply).

Well, I believe it is time to propose Plan B. First, as a longtime boater, anytime marine or boat shops are mentioned, well, we can triple the price of what it ought to cost. So why not take that $300 for a custom duffel (aka duffle, ditty or seabag) for your external-frame pack and, after donating the Tioga to a local hiking museum, buy a decent lightweight internal frame pack with all that money you saved?

Buy a GoLite Odyssey or one of the lighter Ospreys, fill it with lighter & less, and without all that weight bogging you down, you'll find yourself at Philmont able to keep up with that youthful offspring of yours on the trail.

You will probably be getting on a 737-800 to get to NM. You wouldn't think of boarding, with your packs, a DC-3 for the trip. Those DC-3's are quaint, they're gorgeous, but it is time to move on.

Whatever is gained by the back ventilation of an external pack is lost in the extra sweat sacrificed by the lugging the weight that comes with wearing it. Inversly, whatever sweat sticks to your back from a lightweight internal pack is neutralized by the sweat saved by wearing a lightweight modern internal-frame backpack. This is me now arguing with my former self, who wore an external pack for many years . . . until I saw the light.