Air Holes (how many needed?)

[monster]

I bought a 40 gallon rubbermaid for my ball python today, he seems to love it, but my friend said it doesn't look like enough air holes, which got me concerned. I've put 8, 1/4 inch holes on either end of the rubbermaid. I was thinking about doubling that, so hopefully someone can tell me what they think.. The whole reason I bought a rubbermaid is because of the whole humidity issue, because I previously housed it in an aquarium. And I figured the more holes, the more humidity and warmth will escape the enclosure which would defeat the purpose of me buying it. But, will my snake suffocate with just the 16 holes total? Anyways, I was just hoping to clear up or confirm anything. Also, I have a live plant inside with big leaves, so I also figure that there will be enough oxygen provided by the plant, so any thoughts and advice are welcome.