Trying to weld, I’m terrible!
If I'm blowing through easily due to thinness of the old metal compared to the newer metal, I like to pile my welds next to each other.
Conventional wisdom says to space them out on each pass so you don't get the panel too hot and cause warpage. It takes a little longer, but I'll use compressed air to cool my welds and then place the new spot weld directly next to the old one. It makes it more difficult to blow through because the old spot weld is kind of working as a heat sink for your new weld.
I've also never been able to use weld thru primer on the backside of anything I've been welding. I can watch people on youtube use it all day long but it is like straight up weld repellant when I try to use it. My welder acts as if it's trying to weld through motor oil if there is weld thru primer on the backside.