To mig weld it properly you should have tri mix gas and stainless wire..$$
Try playing around some on some scraps with some thin (.023) wire first, you will find that with too much heat, SS warps all over the place, and does not like to hammer straight.
TIG welding works alot better on SS.
IMO, If you are doing repairs on an existing bed made from mild steel, stay with 18 G mild steel.
my signature lines...not really directed at anyone in particular..
BE different....ACT normal.
No one is completely useless..They can always be used as a bad example