How difficult is it for you to get all the pieces delivered to you down there? Do you need someone to help be an intermediary for shipping?
A flag halyard will work, yes. And Dog's idea of taking the weight of the wire on the flag halyard instead of the connector is a really good one.
I'd go with a longer wire than 50', if you are planning to work down in the salon and routing the wire under your hard dodger. 75' would be better, I'd think.
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Average minds discuss events;
Small minds discuss people.
The best minds discuss sailing, anchors, batteries, rode length, fridge-or-not, freezer-or-not, and guns-on-board. I don't know why. It's a mystery!