Welding Galvanized anything makes poison gas...
and to get a good weld you have to burn the metal to get the Galvanization off... thus taking away the properties which you were probably choosing the Galvanized metal for... Catch 22....
Use some good old steel and really consider using the proper rivets and corrosion resistance like the Por15 instead of trying to weld in a floor... MUCH STRONGER.... and longer lasting....