Hi all I use a 25 watt iron but I use a lot of wet tissue as the heat sink. Especially if the stanchions are mounted on a plastic deck which I also cover with wet tissue. In the past I have also made a wood jig with correctly spaced holes to mount the stanchions prior to soldering.
The slight stretch of the handrail brass wire hardens it as well and is a very useful method of dealing with coiled wire. I have used jewelry sources for coiled wire and it is aften cheaper, comes in longer lengths with a good variety of diameters as well.
If you have a lot of bends in the handrail wire to get it in place around the model, I thread all the stanchions onto the wire and then work my way around the hull placing the stanchions and bending the wire as you go.
I once tried theading the wire through afterwards and gave up!
I have noticed in some kits that it is just a square section of balsa under the deck to support the stanchion, I always substitute with hard wood.
Regards
Roy