welding 16 guage metal to 20 guage ,and filler question

i'm splitting a motorcycle tank into two seperate halves it's made out of 20 guage but i only have 16.I already cut the bottom out and replaced it with the 16 welding against the the existing original weld for the bottom.So i'm getting ready to weld the 16 staight to the 20 will that be a problem?Choprods has already walked me through his welding technique so just need to make sure combining the metals will not be a problem.Also any thoughts on the best readily available body filler.I'm in the sticks so not a lot of selection.

 

Good question.
Anyone ever see a situation like this where it looks good at one temperature and then when it heats up "**** happens?
I have seen it when using a Slug/washer to fill a hole.
I always try to get close to the same gage as the original material.
HOWEVER. since you are replacing the whole "Middle" piece, it should be uniform.

 

It's pretty straight forward. You basically pull from the heavier into the thinner metal. Imagine that when the molten puddle forms, you are going to "redistribute" the puddle onto the thinner, kinda making the difference between the two gauges. Is that at all intelligible?