Let's talk about Ash's blister again for a moment... Here is a screencap, hope it'll help locate its exact position on the ship underbelly...
Fred
Here's a quick sketch for development perhaps during lunch hour on my thoughts of it's location to airlock... had to figure out the angles from memory on viewing the film but I'm sure I could tighten up the design...
Space Jockey, your layout is great but I think the blister is in the wrong direction, it should be turned to the left...
Why do I say that ?
Because when the rescue team begins to fade into the distance, Ash shows he can still see them well, he even does a sign with his hands. I we assume the elevator is positioned aside one of the two rear legs, then the blister should be turned toward the front leg, the one Dallas, Kane & Lambert are passing by in the background of the scene...
What do you think ?
Fred