I hereby present you my Sepura Microphone Holder for STP9000 and SC20 TETRA radios.

Just put it over the radios antenna and clip in the microphone-speaker. It is designed fo a snug fit so the holder won't fall off during usage of the radio.

Materials

In general it depends on where you intent to store and use your radios. I personally would recommend PETG as we also store our radios in cars (which tend to get hot in den sun).