A Paper model needs to be sealed , unless you use plastic ( recommended but you need a stencil cutter to really do this justice! ). Sealing just means coating the paper with something that will protect the paper, whilst you add either resin or fiberglass , trying to do either to an unsealed piece of paper is like trying to knit fog !! I use a PVA glue almost any will do the job , use a disposable brush and paint your model inside and then outside with several coats ( two or three coats work best, allow to dry completely before applying the next coat. Then use either resin or fiberglass ( your choice) and do the same - paint a coat of resin or gel on the model and allow to dry completely before repeating - do this until you have built us a hard surface or use fiberglass mating or paper towels inside to build up ( re-enforce) layers until you are happy with the thickness. Then sand smooth , prime and finish as normal . This should preserve your model almost indefinitely - normal wear and tear can be easily repaired by repeating the outline process just on the damaged area. I have a Skywalker Pilot's helmet that's 30 years old - so it will last !!!
