Thommo .. i use a profile design "energy pack" .. can get nearly as much in that as the topeak one i used to use , but it sits much nicer on the top tube. The topeak fuel tank , zip broke after one event .. so money back job (thanks wiggle ) and got this instead .
having said that i do tend to end up taping things on all over the bike and have bags under the saddle and generally go out looking like the cycling equivalent of an SAS landrover .. so maybe i do need something bigger
Oh , i hadn't spotted the slight change in the swim course, I wonder how that will affect things ? if at all ? ... with the quality of my sighting i'll probably still end up having to run round the rock
sounds like you are already perfectly qualified ...See if you can scrounge some pirate kit for race day, the pirate support at Tenby has been epic over the past few years and it really helps you keep going.