Hi i have had the same idea but so far have not spotted boxes big enough for side panniers, however they do exist i saw some in an army surplus store 5 or 6 years ago i think they had 80mm on the sides. I will keep looking.

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XTz 660 tenere, adventure spec bash plate, main stand, skid marks tall screen, Oxford tail pack 36 litre. Kobra hand guards, Bigger cast footpegs, Zen overland luggage plate, USB power point, iridium spark plug, TKC80 f k60 R tyres, o2 and fuel Kev mods, DNA stage 2 filter. bark buster bar wieghts, Touratec side stand base and GPS mount. Led spot lights