Fiberglassing rust in cab

[SawyerBeavers]

So I decided I would go ahead and do a little work to the interior of my 65 cab today and found a little present.. well more than a little..

Welding is not really a possibility for me as I don't own one and I would rather not test my self on this thing. So I thought fiberglass would be a solid alternative, only I don't know too much about that either. Is there some kind of fiberglass patch I can make/buy to put over the problem areas? Ill be wire brushing/wheeling as much of the rust as I can and then using dynomat on the floor of the cab, along with newish carpet.

Any help or advice would be much appreciated. Thanks guys!