I had a CJ5 with a 4WDH fiberglass tub. I always heard that their quality was better than others. I only had one issue with mine and that was the front frame mount on the tub just behind the firewall. Both sides split. But I just went back in with a steel plate between the tub and the body mount and it was fine. I also heard that you should not use body lifts on fiberglass tubs, and that might have been the root of the problem with mine cracking. The Previous owner installed the tub and body lift. I removed it as it looked goofy and figured it wasn't helping my issue with the cracking.
Other than that, I don't have any complaints about the fiberglass tub.... well eecept that when you work around it, you end up itching like hell!