Perhaps the problem is that I am not familar with the CW-80 transformer. In the days of the ZW the U post was the common, or so I thought. I recently discovered that some models of transformer have a different lettering scheme. All of this can make things very confusing.
So, Lionel says that A and B are the same, and track U and accessory U are the ones that are different. OK, that being the case, you should be able to tie A and B together at any point. Then, as you stated, track U should go to the center rail, and accessory U should go to the common on the gateman, as these are the two sources of power.
I’m not quite sure what you are calling the “inside rail”. Track consists of 3 rails. The center rail carries the power. The other two rails are connected together electrically, in the case of Fastrack and regular O and 027, and are both commonly called “outside rails”, regardless of orientation on the layout.
Let’s just forget about the whistle and bell for a minute, and deal with the gateman. You want the light to stay on all the time, and the door to open when the train goes by, right?
Since we have determined that the voltage for the gateman is coming from accessory U, to make the circuit complete, we need to connect the light to a source of that common A B ground. You can take it from the transformer, or tap into the outside rail, it’s all the same.
Finally, in order to complete the circuit for the solenoid, we need a source of that common A B ground. This time we want to use the insulated rail section. The fact that one outside rail is insulated from the other allows the wheels of the train to be the activator. The solenoid needs to be connected to the insulated outside rail.
The whistle and bell activators should have no connection to the gateman, and if you had them working correctly before trying to install the gateman, there should be no difference now.
You aren’t trying to have the whistle blow automaticly are