I welded in drains and my pan halves together. Took lots of time and never welded more than about 4-5" per side before giving the pan time to come back down to ambient temp. I only welded the edge side, I’m not worried about it pulling apart. I used 308L rod for the drains, and can’t remember what electrode, edge seam was just a sweat weld between the two pieces. Instead of trimming the whole edge down I just used a carbide burr and made the slots a healthy V so I had plenty of room to work the tungsten. I’m no pro welder, so I was mildly nervous when I went to water test it, but it has no leaks from anywhere, so I did a good enough job.
The drains I made from a 304 stainless 1" NPT pipe nipple 6" long. Split it and turned it down to be a press fit into the flanged drain edge so I didn’t have to futz around with holding it in place when I went to weld it.
This is before I went back over the OEM corner seam and made sure it was solid as well.
It does a good job draining. This is all the water that’s left after it finishes.
Edited to add that I used the bolts to hold the pan halves together till I had it tacked everywhere I wanted it, then vee’d out the slots. I made sure not to use any abrasives or chemicals that might contaminate the welds in the V sections, thus the carbide burr.