You are much better off using the epoxy instead of hot glue. Hot glue will release if it gets hot enough......seen it happen. There is a product called Duramix you should check out. It is designed to repair plastic which means it is designed to bond to plastic. You should use the Duramix or epoxy to bond the two pieces and as a filler. You can rough that up and then use a body filler to smooth it. Getting the panel smooth and looking good is not the the hard part. Getting the panel to be strong and have proper adhesion is the hard part. Make sure you scuff up all the areas the epoxy will be touching or glue. Making deep scratches in the plastic is like having a bunch of little finger holding your adhesive in place.