JB wrote:

I seem to recall reading that Styrene had the best dielectric properties of
the plastics.

I did some similar experiments building 1/4 wave spikes in a BNC connector
for 2m HTs and found that glues would heat up from the RF. Clear epoxy
worked best and JB weld, Pipe dope, Silicone sealers and Hot glue were poor
performers. I still have some fiberglass tape that I use for torroids.

Of common plastics, Teflon, polyethylene, styrene, and polypropylene
have the lowest RF loss. However, others can be perfectly adequate for
some applications.

Roy Lewallen, W7EL