I’ve done it and it works BUT if you see any way to get it spot weldet by someone then you should go for it and invest some money to get a proper weldet pack.
If you have really no other options take my advice.
-don’t place the sleds upside down in your esk8
-after you’ve placed your battieres onto your sleds, wrap it up somehow using tape or shrinking tube.
-try to not put your batteries out of your sledge to often as it can damage them if you are no carefully enough.
As i said it does work and a lot of stuff ppl. Say about using is not true but it’s definitly not the best way to build a pack.
I don’t understand your wiring diagram so i cant say something about that.
Here is my building thread using sleds, maybe it can help you.