I am aware of the nasties of welding galvanized steel, my primary concern was of crossion issues with 4130 tube. Most of the steel would be used for channels and be tac welded.
The welding on the galvanized will burn off the zinc in the weld zone and you loose the corrosion protection in the weld area. To gain some protection back you would need to treat with a cold galvanizing compound. Galvanized steel does not weld very good due to zinc contamination in the weld puddle. I would just use 4130 and use proper coatings for protection and not mess around with galvanized.
When I was still working as a welder at Charleston Naval Shipyard and going to school we used to call galvanized Japanese stainless. I only had to get sick from welding galvanized once to learn my lesson. The milk deal is an old wives tale and won`t help a bit. You will taste a sickly sweet taste in your mouth and the welding fumes will be yellow by then it`s all over. Fever, joint aches like the flu and general miserable feeling. We all avoided welding galvanized like the plague.
The welding on the galvanized will burn off the zinc in the weld zone and you loose the corrosion protection in the weld area. To gain some protection back you would need to treat with a cold galvanizing compound. Galvanized steel does not weld very good due to zinc contamination in the weld puddle. I would just use 4130 and use proper coatings for protection and not mess around with galvanized.
Oldcrowe, I could find a plethora of galvanized sheet but when it came to regular steel it was a rough go. I did manage to find a source within 100 miles.