[Ria P]

I've never cracked the plastic by drilling holes and usually do three meshed front windows and the lid, sometimes back air vents as well. Just let the drill do its job and don't force it down. The plastic of the Samla is a bit thinner than the really useful box so a little easier to cut. There are tutorials on youtube and some advise to heat a knife over a candle.
If you can borrow an electric cutting tool like a Dremel, it would make life a lot easier. I'd ask around.