Cutting the right holes in the side panels?

[jps]

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...