Yes it is hollow, and no i cannot fiberglass. The other means i have been looking at is bondoing the outer if it is hard after that and i feel comfortable with the durability of him i would leave it be. Since i will be installing a lighting kit and a voice box inside of him. If the bondo isnt making him strong enough i am thinking about drilling a hole and inserting expanding hardening foam to fill him after i did the bondo. Main thing is seeing how he will be after the resin and bondoing is complete. I also need to keep in mind that i don't want him to be heavy due to the fact i am going to have him attach to me and hovering over my armor.