Yep
I agree that you won't typically save much weight over a built-up structure. (The percentage, or even an accurate estimate of what you would save, is impossible for us to predict... It really depends on too many variables in the way you build.)
The main thing that makes glass work worth it to me is repeatability. Once you've made molds, damage and crashes become much less heartbreaking.... More of an inconvenience. Especially true if you've done panel lines, rivets, and all the other stuff that can go on a glass part.
Keep us informed, if you proceed with your F-4. Good luck.