Hi Big-Geoff,
I used a jig for the handrails too, it makes a tedious job much easier. I have been using Bakers Fluid for many years now, and do not attempt to soft solder without it. You are absolutely right, it does not prevent burnt fingers though!! I generally silver solder (braze) any joints that may be under stress, and have found it to be quite easy to do, once I plucked up the courage to have a go. I make my own prop shaft assemblies and usually fit a grease tube to them, I use outboard motor grease, and silver solder them for added strength.
I like your model of the "Portsea", where did you get the plans for it, and how long is it?
Regards,
Peter.