1. Doesn't matter what temperature, as long as its not raining and no crazy wind.
2. Flux core is more for thicker steel plus its too large of a wire for thin guage metal and very messy. A solid .030 or .023 is the best for thin and will provide cleaner results. With patch panels its tacking and tacking, moving around avoiding heat build up, you're not going to be stringing them in one pass. With that said if its is breezy or even in a shop with fans going, I'll sometimes cup my hand around the area being welded, being that its only tacking (wearing thick gloves of course)
