RE: Lets try a splitter board/mold
OK now that you have your part secure in the splitter board lets mold it.
First is to wax the plug and splitter board 5 or 6 times allowing an hour or so between applications. Then I sprayed a couple of light coats and one wet coat of PVA.
#1 I laid out some marks so I knew how far out I wanted my mold flange to be.
#2 This is the surface coat I used I got it from Aircraft Spruce, you can also make your own surface coat by mixing some epoxy and thicken slightly with cab-o-sil and some graphite powder.
#3 This surfacer dries pretty fast when in the cup so I only mixed about 200 grams at a time.
#4 Once all covered let it tack up very well so when you touch it it doesnt come off on your finger. Make sure to smoothly brush it into all of the corners as to not trap any small air bubbles.