Ummm, I shoot my powder at 3mm thick. I dont know what I can do to help you as it wont withstand the heat of the cure at 375 degrees at lowest.
Let me put some thought into this. I can powder coat glass and some plastics with certain powders.
Bondo has small air bubbles in it, which will out-gas (open up) at temps above 250 degrees. I could however apply a layer of high build primer powder on it, this will eliminate the out-gassing. Wet sand after cure and then re-apply another coat just before the base coat.
This will hide scratch marks ONLY by 800 grit sand paper though. Anything lower and you will see the scratch marks. Powder does not fill scratches or gouges it just lies in them.
Let me Bondo something in the shop tomorrow and I will let you know what happens.
Hope this helps you. Sorry to hear that you are having so much trouble with this.