draw your holes. use drill(small bit) and drill alot of holes All the way through the door around hole pattern, that way your holes line up on both sides of the door, then take razorblade/knife to etch out the holes. just take your time. if you use insulated ducting..... say 8" insulated for example, cut you holes 8 inches and just take your time working the insulation part through the holes and they will be light tight.