That's a given!On large gauge wires like for battery terminals or large grounds, snow plow main connections, etc, I use a propane torch and solder with that also after pinching the crimp. There's no way an electric soldering gun could heat those up enough to get a sufficient solder flow.
I use a Uniweld acetylene/air torch with a really small tip but you could use one of those little crack torches that the junkies use to fire their crack pipes. I picked up one of those in a convenience store and it actually does a pretty good job for medium heating and soldering jobs.