Here in the radio shop they ask 27 € for such a (MFJ) thing.
Easily to make itself of a capsule from a hair spray bottle or so.
Firstly I make in synthetic material (ertalon)a ring and place the connector.(PL or BNC)
Solder the wires permanently to the connector. Do not forget putting the the wires through the holes.
Filling up everything with hot glue and let cool down.
If you do not have enough time … put in the refrigerator for some minutes.
Cut antenna on QRG.
Done …
More info and pictures on our website under PICTURES —> HOME BREW STUFF
I always look at the information you post. I do not have direct access to the workshop facilities you have, but your pictures give me ideas and are useful to show to people when describing what I want making.
One problem I can see is that the glue increases weight of your system, while normally you want to reduce the weight for the material carried to the summits. Otherwise the design is robust, though there are probably also other ways to make feed point for inverted V.