Are the cracks in the glass laminate or just in the gel coat?? Most boats will develop crazing/cracks in the gel coat over time. It's because the gel coat is a relatively inflexible medium over a relatively flexible FRP laminate. Somethings got to give when the boat flexes, and all do, and it's the gel coat which develops cracks.
Another problem is thickness of the gel coat. If the gel coat is too thick, it will crack faster and easier. Our old boat had the deck
layed up on a cold day in Costa Mesa. To keep the gel coat on the cabin
sides they kept spraying the cabin
sides as it ran down the sides onto the cabin top, deck was laid up upside down. The cabin top ended up with very thick gel coat that was constantly cracking. I tried grinding out the cracks and filling them but the cracks kept coming faster than I filled them. Finally just bit the bullet and ground the cabin top to bare laminate and painted with LPU, no more cracks.
Another problem is design of the boat. The Tartan 34 classic had very sharp turns where the cabin met the deck. Many of these boats show a crack radiating out from where the forward and cabin sides meet. The only solution is to grind down to bare glass and coat with a more flexible surface medium. FRP likes easy turns to spread out the stress area. It's not that the FRP is going to fail but that any inflexible paint/gel coat won't be able to handle the flexing. In most cases this isn't a structural problem but purely cosmetic. That's not always the case, however. If the bulkheads are right up against the boat hull, they will make a hard point causing the hull to flux at these hard points. Some boats have experienced cracking of the laminate in such highly stressed areas. Anything glassed to the inside of the hull should have at least a small space away from the hull to prevent this hard point and attachment/reinforcing laminates extending out a good ways to spread the load.
In a 125' FRP boat, there is bound to be a lot of flexing. It's inherent in the material. Would be willing to bet you've got gel coat problems, not FRP laminate problems. The first resin reinforced boats weren't FRP (fiberglass) but CRP (cotton). These first plastic boats were built in the late 40's and some were still in surface in commercial
applications when we were building our W32 in '70s. I'm sure someone has done scientific longevity testing but I'm not aware of it. In any case, would bet a properly designed and built FRP boat protected from UV radiation by a surface coat will outlast any of us. My first boat, a Columbia
26, was not a well built boat. Managed to bust the bulkheads loose sailing between the islands in the first year. That boat is still sailing between the Islands 40 years later with the bulkhead fixes that I did almost that long ago.