Well long story short TM hit someting in the water solid. Trolling motor is fine however on my Nitro there appears to be a double thickness of fiberglass and one of the bolts hold the trolling motor went through that first layer of fiberglass.

Now there is no way I can repair it because I cant even fit my hand in there. I have removed the trolling motor entirely. I was wondering should I get some heavy duty fender washers or a piece of plate steel and mount the TM through that under the fiberglass? What are your ideas? Just a FYI you cant tell anything happened from the outside.

Yes use fender washers. Ive always done this myself and my current boat came that way from the dealer.  It really helps to spread that shock around.

Be sure to put a good dollop of marine silicone sealant on the damaged fiberglass and a good ring of it on the washer.

When fiberglass is broken, water can wick into it.  If it freezes, the damage will spread.  Make sure the damaged area is thoroughly dry before applying the sealant.

ditto on the fender washers or plate