Ponton heater boxes

My brothers Ponton is nearing completion and I have started the restoring of the heater boxes. They are made from 53 years old rotten cardboard and a bunch of dirt. I have spent some time trying to figure out how to get them ok. I'll try to cover them with a thin layer of fibreglass/epoxy on the outside and a coat on the inside for water protection. I'll try to glue the metal parts in place after sandblasting them. I bought some epoxy and woven glass at Biltema (a Scandinavian low price car part and tools chain) for this job, as this is about 1/8 of the cost of my boat stuff, and good enough for this purpose. The fabric is 290g/m² and the weave is plain. Twill or satin weave would have been better due to the complex curves but I hope I will manage.

There are two sets of boxes, from the soon finished car, and from the donor car whose life ended about a week ago in a certified car churchyard. One of the sets are previously tried repaired using polyester and chopped strand mat. They are heavy with a rough appearance and quite bad state inside. The other set are original, one is broken in two parts and all the metal parts are quite heavily attacked from rust. I think the latter set is most likely turned into a working set with an appearance acceptable to a rebuild within the standards of this project.