Midwest Custom also builds fiberglass tanks. Their acrylic tanks are absolutely top notch so I would imagine they do a good job with the fiberglass ones too, though I expect the price tag is much higher than those pentair tanks.
Fiberglass Aquariums - Midwest Custom Aquarium
Fiberglass Aquariums Though the bulk of our fabrications are all acrylic, there are situations where a fiberglass aquarium is a better candidate. For larger tanks, a fiberglass shell with acrylic viewing window(s) can be more economical than building the tank from all acrylic materials...
www.midwestcustomaquariums.com