I have chosen to add rudder trim and use the two switches on the stick to control. The problem is the two switches share a common grounds with the other switches ( the hat switch for roll and pitch trim have a seperate ground to allow switching co-pilot trim off) So I needed to go from two SPST momentary switches to a wiring configuration that not only reversed polarity to drive the trim left/right, but also doesn't allow both switches to be activated at the same time. Enter two DPDT solid state relays. The wiring diagram is pictured below. functioning each switch reverses polarity of the current and disables the opposite switch.
Parts are on order from Digikey. Photos of the wiring will be added later.
Parts came in. Wow are these relays small. It took about an hour and a half to wire them up. Then it took another hour to take it apart and rewire it correctly. It turns out I read the pin out thinking it was numbered from a top view, only to figure out the pin out was labeled as a botton view.
Works great! trim rolls in and out and as designed/expected only one button can be active at a time. I will pot the wires in epoxy to prevent movement before mounting in the plane.