ProTec Classic Modding Help!

[DannyUK]

Hi there ladies and gents,

I'm planning on modifying my old faithful Protec Classic helmet to add some arc rails to the side (mainly so I can attach my mesh mask to the helmet) do any of you have any advice on how to do this without screwing up the helmet? The main problem seems to be drilling the hole for the screws without tearing up the EPS foam inside...any and all help would be much appreciated before I go blindly hacking away at my lid :D