I think you're missing the point a bit, when you ask if anyone's tried to devise rules for the game. The whole game is just an excuse for you to do whatever the heck you want, without your players asking why nothing makes sense.
Q: Why is there a well-maintained dungeon under the desert?
A: A dragon put it there to hide its gigaplats from its enemies.
Q: Why is there an aboleth in an isolated 20x20 room on the fifth floor of said dungeon?
A: The dragon put it there to eat you.
Q: Why are we exploring this god-forsaken dungeon in the first place?
A: Because your patron dragon is trying to perform a castle maneuver to net himself an extra 12 brownie points for this cycle and if you don't he'll eat you.