I'll probably update this procedure with a nice PDF document, as usual, but for now you'll have to settle for this.
If you haven't broken your handled transceiver's antenna connector when using a long antenna yet, this will certainly happen sooner or later.
I've faced this problem with my USC230 a year ago, and I didn't want it to happen again on my TYT MD380. Furthermore, the MD380's SMA is a lot more fragile than the USC230's BNC.
So, I've designed a small tube that holds the SMA to FME adapter on the inside, and that provides wide contact area on both ends: my Procom FSP70's antenna base and the MD380's SMA socket.
It just took me less than 2 hours from scratch to draw and print that little strengthening piece. Click "Read more..." to see the result and the gcode file download link: