Not sure if this will help Neil but maybe some ideas.
I recently fitted a pair of "panniers" to my bitsa plunger A10. They are actually ammo boxes painted black. Cheap to buy, cost me $8 each here in AUS. They provide enough space for some tools, a jumper, water proof trousers and a few bits and pieces. There waterproof as well.
Probably not what you are after if you want originality but a cheap way of providing some extra carry capacity.