I'd suggest for that sort of load you'll need four panniers and the trailerAushiker wrote:As to the Surly, I am happy to go with either option depending on the circumstances of the ride. For example on the Dreaming tour I will be carrying up to 30 litres of water at times plus around 14 days of supplies. I have no desire to load up four panniers to do all that.
On our tour up the Oodnadatta Track we were out for 10 days with only minimal supply options at Marree and William Creek. We had all the major foodstuffs needed for that time period plus a day, and sent more food in a package via mail to Oodnadatta. We never needed to carry more than about 10-13 litres of water each (3 litres in bidons and 6-10 litres in a water bag) although we had another 10 litre bag each. The Oodnadatta Track does have reasonable water supplies (if brackish) at bores and waterholes along the way.
I'd suggest that 30 litres of water plus food and other gear is going to be seriously punishing on the bike. A mate of mine carried something like this to ride the Gunbarrel Highway, but that is an extremely remote area. He vowed never to load the bike that much again.