When we did Rubicon, I made a "poochute" out of 4 feet of 4" PVC pipe capped on one end and a threaded plug on the other. It was easy to secure to the rollcage and didn't stink when closed. Just use white pipe to keep the heat of the sun from baking it. It held 4 people's poop for 5 days of wheeling. You can also take a 5 gal pail and a cheap toilet seat to hold bags to poo in. The bucket can also be used to catch fluids if you bust something and need to drain stuff. Cantire also sells a 5gal pail with seat in the camping section. You can also buy PETT bags at the registration for Rubicon.