I'd be VERY surprised if this coach has other than a "rubber" roof. That's what ours has, and I don't think Jayco got very far into f'glass roofs till the last 5-10 years. And then on not all that many models.
On our Jayco of that vintage, the roof starts out flat at the front. Probably because of the way the cabover is formed. The material can be rolled in one direction but not a second direction to form the crown. This is why the little mini-cap I call a "tiara" on some Winnebago's is so important. It allows the roof crown to form at a front cabover whose top surface would otherwise be flat.
Anyway, our roof has a slight crown that develops aft of the cabover and increases toward the back wall of the coach.