I came up with a simple idea to determine the direction of any new tile placed. I drew a little black dot in one of the doorways of each tile. When a tile is drawn, the Space Marines enter through the marked doorway. Simple!
I then dived the tiles into 3 piles and marked the same doorway for each tile in a pile. That way, there is an even distribution among the doorways. I then tried it out and had a straight shot to the the objective room. It then dawned on me that for each tile there was a 2/3 chance of having a doorway straight ahead. Well that blew my goal of forcing a meandering path. For a second, I thought I'd have to redo the tiles!
I then came up with a simple solution. I blocked of the doorway across from the entrance for the air lock tiles. Now, the Space Marines will need to turn left or right after entering the derelict. Problem solved (I think).