ok let's start here. the hinge has to have a bend in it at the top. the door will go sky high if you can get the roll of the hinge right in front of the edge of the door.
ok here are the dimensions of the hinge. I made about 6 sets off of this and I have set in use on my door and one of the guys in our club. i also found you can bend the hinge up to 90 degrees if you have to. whatever gets the roll of the hinge at the front edge of the door.
this is a door I did for one of the guys in the club. It's a full steel slider. still latches with the stock handle and striker setup. The hinges are a set I made. It's 14 gauge continuous hinge. I only use two pieces of hinge 6 inches long each. I trimmed one side to a half inch and then the otherside of the hinge at 1.25" just like in drawing above.
that door has 250 struts but 125 pounders worked for it too. I just got the 250 pound ones at a swap meet for a buck a piece so why not use them.
here is my door. this one is all steel. I did mine a bit lower. I'm 6'4" and I don't hit my head on this so the other door pictured above is a bit excessive but very safe. i'm using 125 pound struts.
here is why regular flat hinge won't work.
I screw the hinge the drip rail with short machine screws.even on the steel doors. Then I weld the hinge to the door. obviously though you will have bolt yours to the fiberglass.
the bend in the J&J style hinge makes the door rotate on an axis lower than the drip rail. hope this helps. let me know if you have more questions.
and just for shits and giggles here is a fiberglass 60 door I made for my van. the glass one is on the left. the plug is on the right.