Any of the patches that I can't access after assembly I put epoxy on before welding in. Like inside the rockers. I epoxied all of that before putting together. Areas that are going to get hidden but need to be welded I put a weld thru primer on. Some panels I use both. Epoxy on the main body of the panel and weld thru on the edges being welded. It's another reason I have to MIG most of these as the TIG does not like the weld thru. It's not perfect but hopefully it will help.Are you going to be able to get back behind all the patches and seal and paint?