install VHF antenna, anyone done it, questions about my mast

You shouldn't have to remove the caps to install the antenna. After drilling a hole for the wire either in the top cap or the mast side below the cap (I have seen both methods)  use a messenger line with a nut that fits the hole tied to it and feed it through the hole. If not tie a small line to something already in the mast, a halyard or wire and use it to pull the messenger up. Add the wire to this and pull both back down. The last time I did this the boat was afloat with the mast up and it went well working from a bosuns chair.

You don't need a long snake, just a new length of stiff fence wire. 
DON'T use a snake or stiff wire if you have internal halyards as it is critical you don't get the new wire twisted round any halyards.  With the mast down, and the halyards replaced by messenger lines, it should be possible to use an existing cable if possible or one of the halyard messenger lines to pull through a new messenger line then fish it through the correct holes with a hooked wire.

When you have a messenger going to the correct place use it to pull through the new cable AND A PERMENANT MOUSING LINE for the next time!

To stop it banging inside the mast use clusters of  three small cable ties at 120 degrees to each other with the ends left long every few feet.  Do NOT over tighten them as they must not distort the cable.

The oversize holes required to get the cable ties in mean you have clearance to put rubber grommets in them to protect the cable at both ends.

It will be quite easy unless you have had an idiot previous owner who has used expanding foam to stop the wires rattling . . . . !!!