When I place down a ship part I need to connect them together. To do this I simply test for any overlaps from a circle collider. You can do this easily with the following code:
Collider2D colliders = Physics2D.OverlapCircleAll (transform.position, .1f);
Here is what it looks like when I place down a new ship part and the PartEditor script auto detects any neighbor parts.
And here is a mockup in the Scene editor to show what the circle collider would look like in the game and you can see the overlaps on the top, right, bottom and left sides where I test for collision.
Now I need to save out the connections and also nest the new part inside of the ship GameObject.