How about finding someone local who is proficient with welding and pay them a few $$$ to come by your place and weld the holes shut for you? Probably take a whole 15 minutes to do both sides of the car.

Better yet have them walk you thru setting up the welder so you know how to do it?

Welding a small hole shut is not in the same warpage risk category as say welding on an entire new quarter panel.