Hi Andy,
Trucker doesn't give many details but we presume his model is based on PS rather than GRP. In any case, a very basic principle of soldering is to use heat sinks either side of the joint with closed clip pliers / forceps kind of thing, crocodile clips, I use a smal wad of very wet kitchen towel sandwiched inbetween. I agree with you otherwise -hot and fast for soft soldering wins the day on a PCB or a brass part! But there are folk equally say to get right temp and go slow. Watever works for the pubic bean holding the iron!
...I have soft soldered pretty big brass parts using a 25w antex. I've never had reason to use anythig else -but again each to their own.
Rich