that is really a great idea, I am going to adapt it a bit to use a thin layer of closed cell foam instead, but a truly excellent idea.I probably made 2 dozen of the speedo gauge pods years ago, I sold a few here.
I made both single and dual gauge pods.
The one in my car is the first one I made.
I used felt tape which is 1/16" thick and cut it about 3/4" long by 3/16" - 1/4" wide.
I adhered one piece to the top and one to the bottom of the pod.
My Aeroforce gauge slides in snuggly and doesn't move at all.
It sits perfectly flush and is centered in the cup.
Don't think you have to wrap tape completely around the gauge.
I'm sure mine isn't the same exact diameter as yours but maybe it'll give you some ideas to try on yours.