Lilibet, I don't know the answer to your question so I checked my archived PC info. The closest I can come to finding out possible sources of info discussing if the PC would disintegrate when exposed to moisture in the soap over time was info on PC for Outdoors and Water use. Don't know if it will contain any useful info. One thing I would caution you against from personal experience....... most of the varnishes used to finish PC (i.e., indoor use Rustoleum Varathane, etc.) are water based and will eventually dissolve when exposed to water over time and oil based outdoor use varnishes are generally not PC compatible, causing the PC to get mushy over time. Hope you are able to find the info you need. Bottom line would be to encourage you to test it out yourself before you you invest too much time.
You might also find something useful here:
www.glassattic.com under “o” for outdoor or
Anita in AZ