Suggestion for holding it together while you work on it (we know exactly what you mean--or we think we do!):
To hold the loose/questionable parts together, put some blue masking/ construction tape across a few places and gently work around them. The kind used for home interior work to mask and whatnot. They hold well for a while (days, weeks, but not forever) and come off nearly perfectly clean. No residue if you don't leave them for months.
Then when that has set, pull those off and fill in the gaps with more fibierglass & resin. Possibly use only mat rather than fiberglass cloth, as it may have more strength.
Paul's becoming really comfortable doing this, and yesterday finished the 2 x 3 foot hole where the fridge
vent used to be, hole #58 out of 59.
Earlier he had to redo an area of the wheel well that also was probably a curb strike. He's used the blue masking tape many times now to hold bits together before the glass could take over, and it's worked very well.
Good luck! Good glassing!