Mounting trolling motor on glass boat

You really need to have some kind of rubber washer or plate backing the bolts or they will eventually pull out and the TM will fall off or rattle lost and waller out the bolt holes. There has to be some sort of faceplate where the TM plugs into that can come off. A few pictures and brand of boat would be helpfull in this.

 

Since the mounting holes are not the same. Going to a minnkota I was able to plug the motorguide holes using 1/4" or 3/8" ? trim christmas trees. A dab of silicone, push into holes.
Minnkota was large enough to cover all but one of the christmas trees.
Like mentioned above. There has to be access thru one or more panels at the front. Tight, but still there.
Drilling fiberglass, use a unibit. Only one cutting edge won't tear/rip/chip like a regular sharp drill bit.
I used rubber washers and flat fenders metal washers.

 

Cut a hole for an access panel

 

I had to do that on my Scout. It was the only way to reinforce the gunwale and to fish tape the power wires. (although mine was in the anchor locker, but in a "cored" boat)

 

That is a long stretch but doable with a small arm. You can always put a dab of something sticky on the face of a wrench and tape to cover the back up, put the nut inside the wrench and a rubber/metal sided washer on the open side of the wrench with something sticky on it and carefully reach up in there . Just make sure to tie a string to the wrench so it won't come off and loop it around your wrist so you don't lose the wrench if it comes out of your hand .

 

They come in many sizes/lengths. Available at wallymart, harbor freight, lowes etc. Get the size you need.
This is only one example
https://www.homedepot.com/p/The-Hillman-Group-3-8-in-Push-Fastener-Retainer-881199/202242476

Yes you could easily cut that opening leaving 1/4" flat space all around for the cover plate/switch plate to sit against. If that makes sense.
Or like mentioned, add a new access hole. Lots of options there. Even making storage if you want.

 

Ahh, the joys of rigging boats. I was working up under the bow platform on mine on Saturday, and at one point my hands/forearms were slightly bleeding in five different places. But when you are done, there’s the satisfaction of having done it yourself. Plus if anything needs to get fixed down the road, you know exactly how to address it in a hurry.

 

I love it! Currently rigging one that’s 1500 miles away...lol

Bought all I would think I need. Hope it all fits in the truck! Tools, 4200, 5200, drill motor, GPS...

Probably the 10th boat, perhaps more......