I've done it the way Kyle is talking about for months as well with no issue. I use 4-way symmetry, start the connection on the tank, then connect it to the engine near the top. It will connect, but sometimes it takes a little finesse.
It's a problem with Unity and high thrust engines. It's been there a long while. Apparently when there is only a single attachment joint and a high thrust engine (causing high forces) unity has trouble dealing with it and it causes the wobble. If you strut the engine to the tank, it gives it more connection points and Unity handles it better.