I have been looking into resistance soldering for rail joints. I've looked at the Micromark ones, they seem as good as any. I decided I'd rather build one when the time comes. I originally saw a how-to in an 80s Garden Railways mag. It is very simple, and the most expensive bit is the power supply. I'm planning to use an old battery maintenance charger, with a sewing machine foot pedal for a switch. You should be able to find a how to video on the web. If not message me and I will try to locate the mag and scan it for you.