Might be a silly question but...is a drilled airbox something that needs to be declared on your insurance? I haven't done it yet but wondered if it needed to be declared and how much more it might cost on the premium?

All mods should be declared. Ask your insurer whether it will add cost before you do it

I'm with Vickster on this. Tell them you are thinking about doing it, but whether or not you do will depend on how much it adds. They might not like the idea of doing the paperwork for no additional brass and that gives them an incentive to just let it pass - its not like you're upgrading the turbo so the value to them is likely to be negligible anyway.

I'm gonna give 'em a call in the morning.