I never realized this was a thing. I guess I would consider myself an ex-pro padder. Before I had a belly of my own, my fake "fat belly", that is realistic enough to wear in public, started with a silicone pregnant belly costume (check eBay, it was about $100 though). They weigh a lot, are jiggly like fat, perfect belly shape complete with belly button. The only thing is the straps blow- I had a shoulder strap break causing my belly to sag once. Lol
To solve that problem and hold the thing in place, I used a bra-less spandex slimming top thing.
I wanted to experience "fat humiliation" before I gained weight, and would go to a mall, usually the next town over so I wouldn't risk running into someone I know, and hit up all the places to get snacks and wander around stuffing myself.
Now I can just wear an old shirt

That's my first memory of being interested in becoming fat, just didn't understand as a kid.

Intrigued, could you elaborate?