Ok time for a progress update. It's taking longer than I wanted to get this done, but it getting much closer now. I spent a day or two trying to make the mold for the back. Took a bit of figuring out but eventually I came up with this.
It's the 3M foam insulation board, I cut then pieced it together to make the right angles. I Then hand sanded everything to get the shape a bit better and finally use some silicone caulking to fill in the seams and act as a filler to better round things off a bit. I then covered it all with some wood glue to try and seal up the foam.. (non epoxy resin melts this stuff) I also uses the car polish for the release agent as I've been using all along.
I read somewhere online the wood glue will stop the foam from melting, but it appears either I didn't get good enough coverage. The foam did melt but it took long enough to do it that it didn't cause any issues.
Here is the patched in panel right after removed the foam mold. I didn't bother using a gel coat because I know it wasn't going to be perfect and would require some fixes on the outside.
I did decided to add a bit more support to thicken it up on the inside where it will be cut and rest on the van roof. When fiberglassing it all in I used a mix of angel hair and heavy mat. Seems to have worked pretty good the area seems just as strong as the rest of the top.
Last a up close profile picture because it's pretty hard to get a good picture that shows the actual beveled lip. It's not perfect but I'm pretty happy with it. I ended up doing a bit of grinding on the outside then ran a few strips of fiberglass around the edges to glass everything together real well.
I will wait till tomorrow to trim the edges then I will do a test fit. Once the test fit is good, I'll start on cleaning up the outside and cutting out the windows. Hoping to get some paint on it in the next few days so I can be done with this and finally move on to mounting it and building the van camper interior.