In an obscure little section of the manual about not carrying a fuel can, it says that if you must carry a fuel can store it somewhere safe "like behind the rear seats".
Ah ha, I thought, some storage space I've not yet found in my new acquisition!
Folded down the seats and there is just a neat back wall that seems well fixed in place. No space.
So have I misunderstood something? It's a C4, so perhaps the manual's comment only applies to the C2.