Yeah, I was figuring close to a gallon a day for drinking and cooking, which is about 3-1/2 L. My plan had been to park at Chisos, work my way down toward the South Rim for a couple days (hitting Boot Spring, climbing Emory Peak, etc along the way) and then depending on terrain and what I see from the South Rim, maybe bushwhack my way cross-country down toward that Outer Mountain Loop and then use that to get over into Juniper Canyon which would lead me back North. So no, my plan is probably not sane; but that element of potential tragedy is my favorite part.
I really hadn't even considered caching water cuz I always try to avoid any roads/people/etc when I do this stuff; do folks just drop gallon jugs of water at places where a primitive road touches up against that Outer Mountain Loop? Are there some kind of modified bear boxes there to use? Are there issues with jackasses stealing other people's water? Caching is sort of an intriguing idea in that kind of environment.