I used a similar technique of free motion and locking it square on the center of mass. Additionally, I built a ship that has 4 RCS grabbers just off the top (Claw, 2 medium RCS tanks, remote control core and 4 RCS ports. I come up on an asteroid, impale it with a couple of the RCS pods and then attach the main tug and align. Even with it a little off, the RCS will keep it aligned during burns and makes turning the thing much easier. Once attached, it sees the whole thing as one big ship and will use the RCS pods as needed as you can see from a couple pictures I took the other day. Only used this on class C so far, works like a charm. Edit: bah, I'm a newb when it comes to Images. Thank you Padishar