Cutting the right holes in the side panels?
 

I'm going to trial fit my fibreglass side panels and am a bit nervous about cutting out for the front suspension mounts, etc.

Any tips on how best to work out exactly where the holes need to be?

The panels seem a very close fit but not 100% (not that I wish to open up any debate about whether the panels, chassis or both are slightly out on dimensions!!). But because of the differences I don't want to assume the panel is the exact correct length and base any cuts/holes on a "measure x cm back from the front edge" technique...

Cardboard is a lot easier to mock up with and a lot cheaper to replace if you get it wrong, cut the card the same height as the chassis and mark where the edge of the card comes on the chassis. Draw round the suspension brackets and cut out untill your happy with the wishbone clearance, then measure and mark out your side panels and cut them.