Is modern fuel OK in an alloy tank, I know there are issues with ethanol and was wondering if I'll need to coat the inside with flowliner or something similar. 

Appreciate any info cheers

Not in my experience. No need to coat.

Edited February 29, 20206 yr by b40rt

I had an aluminium tank that had developed a line of corrosion holes in the bottom of one side which were in conjunction with the gum that forms when modern fuel is allowed to evaporate in-situ. The corrosion holes were under the gum. I suspect that there may have been some water also present during the hole-forming process but by the time I got the tank it was dry and just had the gum and the holes.

If you don't allow things like that to happen to the tank, aluminium is one of the best (longest-lasting and lightweight) materials for a fuel tank. I've seen zero corrosion damage on any other aluminium trials bike fuel tank.

Thanks for your reply, had a load of bits floating around in an old Tlr tank once so thought it was worth checking out.