Re: Install Cleat - No Access Underneath.
Here's my suggestion: just screw the cleat(s) into the fiberglass without backing, with stainbless wood screws made for this purpose (securing cleats). Sure, backing is better, but you aren't going to lift the bow by the cleat; all force will be perpendicular to the screws.
Then, don't use that cleat for any real force, such as towing or obviously lifting. For that, use the bow eye, which is stronger although less convenient, for being towed or anchoring in adverse conditions. But the top cleats are convenient and fine for fair weather docking and anchoring. If you ever take the boat to be worked on off the trailer (eg bottom painting) warn them not to lift it with the cleat.
Further, don't mount the cleat dead center in that boat; your passengers loading across the bow will stub toes, catch flip flops, etc. Put them on the side on the top of the gunwale, which is probably stronger as well. Use nylon, not stainless, cleats b/c they don't hurt as much when you kick them, and they are more obvious as being low-strength.
Then, if you think you need it, make a 4 foot extension with a solid snap hook on each end, to hook onto the bow eye and then bring up into the boat and attach your anchor or tow line when strength is needed.
I have been using what I believe to be non-backed cleats for years and often with some very heavy force, just not straight up as to the screws.
