"Jan Carlsson"
:

You can probably make a little bigger tank in composite, I have made 2
using wet lay-up over a foam plug, ((one with plastic cover material
for buildings) and one I put gasoline in the foam and scraped the gunk
out) no foam sandwich in the walls, and a couple bulkheads in the
tank, and a large sump with drain and outlet for the fuel line.

Used 3-4 layers of 300-400 gram fibre glass, the epoxy is about the
same amount as the glass.

OK thanks. Nice to have a few figures to work with. I can see there's no
weight advantage, definitely.

Thanks again to all! Any other weight saving suggestions welcome, though!