Welding the hull on new aluminum boat with mig gun.
The aluminum is 5083 h116. 1/8 thick, should I be using 4043 or 5356 mig wire

5356...it's stronger and has proper amount of magnesium in it for 5083. None critical stuff you could get away with the 4043.

I've used both. $043 is more flexable or ductile. It has been said that 4043 is not the choice for hulls in salt water. We I live about 90 min from gulf and most builders use 4043 and haven't had any issues.

Now, in my personal experience, 5356 is a harder material and depending on what and how you are using it, it is more prone to crack. But again, that's my personal experience.

I'd buy both and on ribs and hull seams I would only use the 5356. On decking stuff you could probably choose either. That 4043 welds easier with the thin stuff like decking.