Rafters on Grand Canyon trips (which can last up to 20 days) often freeze food, put it in a cooler with dry ice and tape the cooler shut until the food is ready to be used. Even in the summer with temps over 100 degrees, this works well and can keep you in fresh/frozen food until day 10. Gotta admit, though, that week three on a Grand Canyon trip is not as much fun from a culinary point of view!
Just found a great Web site
http://camprecipes.blogspot.com/
with information on packing and cooking for river trips and just talking about food. Raters love dutch ovens! and Nutella! and he includes some interesting recipes.
Anyway, scroll down to the June 9th entry on camp tips on river rafting trips. There is GREAT information with many take-aways for teardroppers, especially if you are doing multi-day dispersed camping.