I think the first question from our end would be: What sort of FGRV are we talking about? This impacts the responses with regard to bracing afterwards.
As for the fibreglass repair, this is fairly easy. There are many easy repair kits out there. My personal preference is West System since it allows the user to dispense correct amounts of hardener and resin that can be used in the proper time frame.
If the break is in a hidden place inside the trailer, then a contoured plywood support which is fibreglassed to the interior wall would probably be enough to provide some protection should the ladder get re-pushed in. Otherwise, a good repair of the broken area using fibreglass should be sufficient.