Side note about welding metals of differing thickness. One thing you can do is to try to keep most of the heat and weld on the thicker metal and tack it over (sew it in) onto the thinner metal... OR, what I usually do, is to set the machine for maximum penetration on the thinner metal that I can without burn through, and then just weld it like I normally would any seam. Theory there is your weld connection is only going to be as strong as your lightest material used, so if you are welding 1/8 to 3/8 and it is going to break, the 1/8 will give way before your weld OR the 3/8 will anyway... Hope I'm not being too confusing.
In simple terms it all goes back to a chain only being as strong as its weakest link. No matter what kind of filler you are using or what the tensile strength is, the union will only hold what the base metal is capable of.
BTW, your project looks great! Keep us posted on progress
BBQ ADDICT and Ag Teacher