http://cvrpg.com/images/comics/comic1195.gif
Nice. I'm just wondering... what's the benefit of sleeping in a coffin?
... except by people named Lora or Indy, you are less likely to be disturbed?
Well, it depends on if, in Castlevania lore, a vampire needs to sleep in his homeland's soil. An easy way for a vampire to do this, and avoid the light, is to crawn into a soil-lined coffin.
That said, Darkmoon doesn't exactly have to avoid the light, let alone much else... so maybe it's just force of habit.