Anyway, three days later with input from fellow cruisers, lots of rewiring and insertion of two in-line fuses as isolators, and the charge going directly to the batteries, we seem to have settled the fluctuation down a bit. We are monitoring the situation but a local solar panel expert seems to think it should be okay.
On a good note, we needed to have an AIS transceiver for the world ARC instead of just the receiver we currently have. I fitted the new wiring yesterday, including a separate switch to be able to run silent without transmission in areas where we don't want to be seen. We needed a cross-over cable (120 eastern Caribbean dollars) to tmake a link to our existing network, but once installed, it was bingo! I scooted across to a neighbouring boat in the anchorage to find out whether they could see us and yes, a tick in the box. Something went well for once.
Tomorrow is US Thanksgiving lunch at the local hostelry, we are making brownies and roasted vegetables as our contribution. It will be nice to do nothing for a day.
Another good note is that we are nearly there with the canvas work and it's looking great. We have a dry cockpit area now which will be a real treat!
Somehow it feels that we are finally getting sorted. We still need a couple more things fitted and we are good to go sailing!!!