Into the tubes went new MSR 30 oz. fuel canisters. Excellent quality product made in the Pacific Northwest. These cans are seemingly made to fit into the tool tubes. Very little wiggle room. I bought a filtered funnel to fill up the canisters and now I figure that I have a reserve reserve half gallon of fuel available when I think the ride might call for it. Another 35-40 miles? Gonna ride test the set-up tomorrow. Overall cheaper than the rotopax.