Not much difference between mowing an outdoor map and mowing a dungeon map, IMO. The biggest issue to a seriously long dungeon run is the need to peck at it. Whether you have to do a bit, go back to town for supplies, and then do more; or do a bit, go back to town to sell loot because you can't carry anymore, and then do more; or do a bit, go back to town to resurrect the dead cuz the dungeon is a real bitch, then do more… And locking the party in the dungeon to eliminate the backtracking without eliminating the issue that prompts players to backtrack in the first place is even more annoying.