I have this arrangement on my GK24, the shrouds act as a good broadcast radio aerial.
This works well with my vintage 1970's Sharp car stereo I fitted.

However, with a modern MP3/CD radio combo, the radio was useless and unstable with wierd whistles and burbles on Radio 2, the only station it could recieve.

So I went back to the old stereo - after all its more in keeping with the 1979 boat.

As for chocolate blocks, B&Q sells them for various prices from 99p for two made-in-china versions. Searching the electrical shelves nearby shows others priced higher.

Otherwise try an electrical/builders wholesaler.

It is held that a good crimped connection is probably more secure, but I have made some crimps that are worse than a chocolate block connection, usually with the wrong sized wire involved.