Raymakr: Are you planning on this water can being full or empty? Big difference in weight, big difference in how you would mount it. This is a "field mod" obviously and those usually require poking bubba holes through your jeep. If I were doing this, I would study such "field expedient" photos from WWII to see what the doggies did. Probably the minimum to keep the can from falling off would be my guess. I would probably get a jerry can holder(bracket) and mount it on the step through the bottom and into the jeep tub through the back. A hunk of flat steel bar as a backer for the bracket bolts would help in keeping them from pulling through the 18 gauge sheet metal. Running the strap up through the eye bolt, as you suggested, would probably work.
1/4 INF, 3rd ID - Aschaffenburg 1976-79 (11Bc2)
1943 GPW Louisville in restoration, on hold
1944 GPW Louisville-matching #'s in restoration
1945 MB Original
1945 DUKW (sold)
Red Bull Historic Military Vehicle Assn http://www.redbullhmva.com