Well, that's a cool idea! When you said PVC mold, I visualized a long round tube. This would be so much easier to work with, IMO. Thanks for sharing the idea.
Do you have any problems with soap leaking out?
I pour at a thick trace to make sure none or very little escapes If you have a perfectly flat baking sheet/whatever you put the molds on and perfectly flat mold bottoms, I wouldn't think you'd have any issues as long as you weren't pouring at a wicked thin trace.