This morning I decided to disassemble the stock L92 connector to see why GM didn't use any cavity plugs. When I removed the bottom TPA(ecm side) you see no evidence of any cavity plugs. Once I removed the top TPA I could see that GM has the cavity plugs molded into the TPA. I also noticed that the GM connector parts numbers are difference from the 73 and 80 pin connectors that are commonly used in the aftermarket.
Here is a pic of the top TPA.
Also, if you use a release agent with your potting compound you can make your own connector. It's not ideal, but it will work if you have no other option. Your module appears to be mounted in a location that won't see much moisture/water anyway, so I don't see you having a problem with the foam method.