I've recently bought a US20 + 2xUS10, with the thinking that I can get 10, 20, 30 and 40 out of that if need be. My plan if I need an extra bit of space is to get their Overlander 15's and run them down the sides of the seat for a total of 70. The 20 behind me when riding is super comfortable, I've used them a lot the last few weeks and I'm already used to the strapping/unstrapping so I don't find it bothersome. No idea with the bigger 30/20/20 setup though.

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Josh
Perth, W/Australia
2010 XT660Z Tenere - 1982 Honda CM250 - 1979 XS750