Lead solder works, but you have to use acid to flux the steel and reinforce it with wire and a long contact surface. I generally silver the heavy wire before assembly. Silver solder is way stronger, but you need a hotter torch (oxy-acetylene or air-acetylene, maybe oxy-propane) and have to be careful not to overheat the wire and soften it permenantly. I have used silver solder on wheel and float struts successfully with just a simple joint - no wire wrap or other reinforcing.