Well, I finally figured out where I had seen the tip for mounting a Trolling Motor. Here it is for anyone interested. It came from BassBoat Central.

Bow Mount TM Install (Tip of the month for December '04)
I took a 3/4" piece of marine plywood, marked and drilled my holes to match the trolling motor base. I placed it under my deck for fitment to see that no corners need to be clipped or rounded etc. Once fitment was proper, I took threaded "T" nuts and drove them into the holes where the bolts will come through. I then dipped it into polyurethane several times to completely seal it. (Let it dry before each dipping). Also, I plugged the threaded portion of the T nuts so they didn't fill up.
Once it was all dry, I smeared a healthy dose of silicone adhesive all over the face, or the part that would be resting under the fiberglass deck. Have your trolling motor in place and put the bolts down through and tighten them into the threaded T nuts. This will suck the plywood and the silicone adhesive tight to the underside of the deck. Let it dry for 24 hours.
Once dry, you will find that you will never have to go under the deck again to grab a nut to remove your trolling motor. The plywood is securely attached to the underside of the deck and the holes are all lined up each time you remove and re-attach your TM. It also adds lightweight but sturdy reinforcement to the fiberglass deck. If you are worried about your bolts loosening up, try using a little dab of Loc-Tite (Blue), it is a removable thread locker and will hold those bolts tight until you are ready to remove them.