Nice job! I assume you're backfeeding the new panel through the 50 amp double pole? I did that in my last TT. It was tripping the 30 all the time so I moved the A/C to the new leg and used the old panel as a sub just as you did. I also added a new wall mount 120 volt heater to the same 20 as the A/C. You're never going to use the heater and A/C at the same time so I stuck them on the same breaker. That panel probably accepts piggybacks if you ever need more spaces. I guess you knew not to bond the panel? It gets bonded in the CG panel.