you can use my tank with pleasure mate if it helps at all being 200miles apart?
wouldnt a plastic tank, i.e abs/injection moulded end up heavier than the stock steel?
motorbike tanks tend to get away with it due to their size and more importantly their strength and rigidity down to their shape which is very multiplaned. (a poor explanation!)
but a big rectangle box full of fluid would have to be very reinforced to be built at this scale, and very thick walled too, and i'm pretty sure thats gonna add a fair bit of weight.
plus, you've then got to integrate reinforcing and threads etc for the pump, sender unit, etc, which again is much tougher to do with a plastic tank, and i suppose ultimately, tooling up for this process is pretty costly i should think.
as you'll mostly know, plastic is not my choice of material to work with, so i could well be off the mark here, but i should think that alloy is the best way forward here.
my two penneth anyway!
cheers all, hope you all had a good crimbo, and lots of italian car parts off santa!
ps - all the best to everyone for the new year!