For soldering, I find the bigger the iron, the better. Long bits of metal like masts will conduct the heat away from the joint area really fast, so you need to get a lot of energy into the joint to melt the solder AND get the parts to the same temperature as well. Are you tinning the parts first? After cleaning them very thoroughly, wire wool is good for this, IMMEDIATELY apply some flux to protect the metal from finger grease, oxidation, etc. Make sure the iron tip is hot, dip it in the flux, then apply your solder wire to the tip; it should melt straight away, and provided the iron tip is clean and fluxed, the solder will 'wet' the surface. If it stays in a little molten blob, or worse, drops off, the iron is not clean enough, or fluxed. Put the tip of the iron on the part, firmly, and wait for the heat to spread into the part. The flux will start to boil and smoke, and then the solder will 'wet' the part as well. Carefully wipe the soldering iron tip along the part, leaving a bright, clean skin if molten solder. Remove the iron, and repeat for the next part. Again, if the solder forms little droplets rather than a smooth bright surface, the part was not hot enough, and/or the part was not clean or fluxed properly.
Once you have a coating of solder on all the parts, you can place them together, dap a smear of flux on the contact point and just apply the soldering iron again. The solder will melt on both surfaces and flow together. Remove the iron, blow gently o cool the solder and bingo, joint jointed.
I'll take some pics if anyone will find them useful.
Tim P