look into aves apoxie sculpt.
Mix A and B together and you got 1-3 hours work time before it hardens, Then you can sand and scrape it etc...
Sculpty you need to back to harden and with PVC you will warp that stuff cause scutlpy needs to be backed at like 375 degrees or something like that. PVC wont stand a chance in a oven or even being boiled in water.
There might be some clays out there that air dry but they may have a % of shrinkage to them when dried and may mash up a PVC specially if its a hollow PVC. Then you run into cracks on the shrinkage.
I have baked sculpty in my oven and food after never seen a issue with it.
Sculpty on resin in a oven is ok, but PVC would be scary to even try it since its a softer plastic.
Hope some of that helps.