I actually want to talk about what beds the Winchester's sleep in, specifically:
DEAN DOES NOT SLEEP IN THE BED CLOSEST TO THE DOOR.
There's a pervasive fanon out there that thinks that Dean always sleeps in the bed closest to the door. Now, this fanon persists because it's adorable and protective...Dean sleeps by the door to protect Sam from whatever might come through the door...awww, the love.
Sadly though, it's not true. While Dean has slept by the door in episodes such as Mystery Spot and Phantom Travler, we've also seen him using the bed furthest from the door, such as in All Dogs Go to Heaven, Salvation, and Scarecrow (to name but a few). The Winchesters seem to chose which bed they sleep in at random.
Now, that being said, in a lot of pre-series fics, Sam and Dean share a bed. This IS supported by canon.
In Something Wicked, John leaves Sam and Dean in a motel room that only has one double bed. To me, this means that not only did John rent the motel room JUST for Sam and Dean while he was away, but he also didn't bother getting them one with two beds...which to me means that it is likely when John was with them, that he'd rent rooms with two queens, and take one for himself and leave the other for the boys.
So, to recap:
Dean sleeping in the bed closest to the door: Fanon.
Sam and Dean sharing a bed when they are kids: Canon.