Roof Top Equip Mounting Question

[76SeaRay]

I am laying out my roof top equipment and wondering about through bolts or screws. The boat originally had a hailing speaker mounted to the front windshield frame and horns down on the deck at the bow. I decided to clean that up and move them to the roof top so that I don't have lines fouling in the equipment. This is a picture of my planned layout. I am planning aft deck flood lights and port and starboard docking lights. I also am adding an AM/FM antenna (fold down, an anchor/nav light (fold down), and a fixed mount GPS antenna to the top (none originally on the boat). As you can see in the pic, I placed the horns and the hailing speaker (a bit larger than I thought when I bought it) on the top. The hand rails shown in the picture were originally on the top and were through bolted with no sealing material. There are reinforcing plywood strips that were used to attach the head liner but the mounting of the hand rails did not go through those. Now to the mounting....

I am thinking about adding 3/4 marine plywood backing squares at each piece of equipment on the inside of the roof, drilling mounting holes and then filling with structural putty. I would then drill small pilot holes, lay down new gelcoat, then drill and mount the equipment with stainless steel screws. I would set the screw lengths so they don't go completely through. I am wondering about the strength of mountings with screws instead of through bolts. The hand rails and the AM/FM antenna would be the biggest concern. The GPS antenna came with 1/4 inch mounting bolts but it is low profile and likely little wind resistance.

My VHF and CB antennas will be mounted to the sidewalls of the lower hard top behind the lower windows (see profile pic) on each side using swivel mounts. Those will be reinforced with 3/4 inch marine plywood but will be through bolted.

Thoughts or comments on the mounting or the use of structural putty to fill the holes for sealing?

Thanks...