FWIW, the FJR's seat retention isn't all that great. It's already been stated that a seat pan based fuel cell attachment would not pass the Warchild testing procedure. You could fabricate a pan that fits where the pillion seat goes, but is retained in a more secure manner, (bolted down to the subframe).Thanks Chaz, it is a very sweet ride.
Prolly the same old Aux tank. Thinking about getting an extra pillon seat and making it a permanent mount on that and then can swap 'em out as I like.