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.
Fun fact #2484: In my avatar, that's DavidPM at the helm of my boat.
Bland, non-political statement goes here.