Jack442

This is what I use. Works good for me so far.
https://www.dxengineering.com/parts/dxe-wpcc88-1

You can use dielectric grease on the threads only. Don't let it get on the outside of the connector and the center conductor at the same time. Or you can use vaseline on the threads only too. Best is to wrap it with self sealing rubber tape.

Yes that is one brand. And it is a very good brand the makes some of the best coax cables.

I would not use RG-8X coax. it will have too much loss at GMRS frequencies. RG-8X is for HF frequencies. Your best bet is to use LMR400 or equivalent.
Here is a good thread on coax loss. https://forums.mygmrs.com/topic/252-cable-types-and-losses/page/5/#comment-69960
RG-8X is not listed. But it generally has more loss than standard RG-8

Thank you @Sshannon That is exactly the info I need.