Late adder here but..

RT3 is great   battery is a beast.

I also have ram mount 8″   It really doesn’t fit the RT3 correctly and with the help of some foam strips would be great. I may contact Ram Mounts  as it would only require some new molded end pieces or some inserts. It just doesn’t fit great into the end caps and it can me annoys me.

I made my own adapter to the 12mm bar using a generic mount clamp with 4 holes and a 6″ piece of 2″ wide 1/8″ thick aluminum. Nice and solid.