We purchased a figerglass front door and installed it last fall. The door warps.
Is this common? We researched it and found out that all doors will warp if you don't seal them. From what I read, it seems like gaps are created when the sun shines on the door. Then the gaps go away later in the day, when the sun goes down.
Will sealing it this summer prevent it from warping in the future?
First and foremost, fiberglass will not warp. What CAN warp is a door frame if it's not properly installed. But if the door is installed in accordance with the manufacturers' instructions, it shouldn't be having these problems. I suspect your door needs to be removed and rehanged.
Another possibility is that the opening to your home is twisted, which could also be causing this problem. A skilled carpenter can adjust for that when installing a new door.
Another thing to keep in mind: Fiberglass doors don't need storm doors. If you have one over it, the excess heat generated between the storm door and the fiberglass could be contributing to the difficulties you're having. Above all, though, the concept of sealing a fiberglass door is unnecessary. It's not porous, and therefore doesn't need to be sealed.