Another technique for sorting out weld lines is to paint areas of them with liquid poly, since it works by effectively 'welding' plastic parts together, it attacks the plastic and softens it without the application of heat, takes a bit of experimenting to get the technique, so if you try it, do it on a bit of scrap first, but it works, sort of similar to making filler by dissolving bits of sprue in liquid poly.
Careful you don't go over the top with it though, lumpy welds with pinholes (in real life) would be considered poor, because they would be weak and not fuse to the base metal. The hallmark of good welding is for it to be smooth. Professional welders refer to poor welds as 'pigeon sh*t', because that's what a poor weld line resembles, one good whack with a lump hammer and a weld like that is off and in bits on the floor, I know this because I was taught to weld by a guy that used to do it on rigs at sea incidentally, and he used to take the p*ss out of my first attempts mercilessly! And don't forget, the Germans were way ahead of most nations in welding techniques even in WW1, as evidenced by many of their aircraft using steel rather than wooden sub frames, so their welding was generally very smooth indeed.
That soldered mod looks good by the way.
Chock