Why is burying yourself not such a great plan?

One of my player is a clever guy. At night when the others are putting the camp together he digs a hole big enough for himself (between 3-4 feet deep) and asks someone to cover his body with dirt; he then uses a straw to breath. His idea is to avoid ambush at night.

The first time I was baffled by this idea and had no response. After a couple of nights I started challenging his strategy. I identified a couple of potential complications but he was able to answer everything I offered.

  • Sleeping under 3 feet of dirt at night would be terribly cold (But I have a bedroll which is warm enough
  • You wouldn’t sleep comfortably and be sore in the morning (No specific rules for sleeping in armor I can use as a reference)
  • Breathing through a straw requires keeping your mouth closed and doing so while you’re sleeping is impossible (I’m an elf and when I’m in trance I’m not asleep so I can keep my mouth shut)

    He has no intention of quickly being able to help the rest of the party if they get attacked, so escaping his hole is not something I can use against him (I tried).

    So far the problem has not transpired out-of-game. I’m annoyed because he’s obviously trolling but the other members of the group don’t mind his selfishness (he doesn’t get XP or loot from attacks at night).

Am I wrong to think that this is not such a great plan? I can’t think of any reason or mechanics to point out the flaws of his plan.

I don’t mind him doing it. I just think I’m not emulating the consequences properly because it’s an obviously stupid decision.