rear fiberglass hatch repair

Okay, heres my problem. I just got an 88 RC, and the rear hatch is cracked pretty bad on the passenger side right above the top corner of the window. It is starting to crack on the right side. The crack is only on the outside, but it lets the door hang down almost to the point where it wont close. As it is, I have to lift on that side to get the door shut.
My idea was to remove the door, and with a dremmel tool grind down the cracked area, and a couple inches on either side, to about half as thick as it is now, then fill it in with some fiberglass repair stuff.
My question is, would this securely hold the door, or would it just break again as soon as it was under stress? I was also thinking of just realigning it, and pop riveting a piece of sheet metal on top of it to hold it together. I know it would be ugly, but sometime in the future I would replace it anyways.
If I dont fix it soon, Im afraid it will crack all the way through to the piece on the inside, then the whole door would just fall off.
Does anyone have any other ideas on how to fix it, or any other comments on how this fix would go?
Thank you in advance,
C.J.