You're going to need to somehow access the condition of the wood framing underneath the fiberglass in your RV to assess the level of moisture-related damage. If it were me, I would first go up on the roof and use my hands and feet to see if I could detect any soft spots. If some exist, you could always access them (to repair the damage) via the headliner (from the inside). On the other hand, if the level of damage to the roof seems widespread, you might be looking at a bigger job that involves the removal of the fiberglass roofing (to access and replace structural members).
In any case, once you determine the level of damage, you can then develop an appropriate strategy for fixing it up and re-mounting the visors. The trick now is to learn more about the underlying condition of your RV's roof. Hopefully, the damage will be minimal. Let us know how things work out.