Fiberglass machined hole repair

I'd pass on that kit since it's polyester. Bondo makes a cheap epoxy kit you can buy at most auto parts stores or walmart. It would be best to post a picture of the hole you are trying to fill so we can advise you most accurately. Shouldn't be to big a job, biggest issue will be what are you planning on painting it with?

 

Do you have access to the bottom of the deck from the hatch?

Where are you located?

 

*Sand and clean the bottom.
*Take a piece of wood and cut it slightly larger than the four bolt holes and cut a piece that you can use to wedge it tight up to the deck through the hatch.
*Grind the top so that there is a slope/taper going toward the hole
*Cut a piece of wood that will fit in the hole (exact fit not necessary but make sure the wood is below the top of the deck because you will use glass to level it.
*Cut several pieces of glass in the shape of your grinding where each piece is slightly larger than the next.
*Dry fit everything ensuring the top will be level when you are done.
*Get some epoxy and 6oz cloth
*Cut a piece of glass to size for the bottom but smaller than your wood
*Mix epoxy and paint the repair area underneath and wet out the cloth and position it to the repiar through the hatch, put a piece of wax paper over your wood you cut and set that up to the repair and wedge it so it won't fall down
*Thicken some resin (no activator yet) and get it thick like peanut butter and now add the activator and thicken again if need be and slobber it over the wood plug and stuff in place so the all the space is filled with the thickened epoxy and oozes up as you push it in place
*Scrape any excess off and wet out your smallest piece of the circle of glass you cut and put in place.  Repeat as many times you need to get it flush to the top of the deck
*For the small holes just fill them with thickened epoxy
*Done

It appears that you have a no slip deck.  This will be nearly impossible to exactly duplicate without a ton of work.  But there are a couple ways to accomplish the same result.  Tape off an area and sand it smooth.  Wet it out with epoxy and sprinkle shark grip (HD or Lowes) to the desired texture.  Another way is to start in the same manner as described.  Find a sponge that is used for grouting and a piece of saran wrap.  Wet out the area, stretch out the saran wrap over the patch and tape in place, place sponge on top and lightly weight the sponge (a brick is sufficient).  It will leave a texture that mimics the surface of the sponge.  Either way, paint and enjoy.

Dry fit everything first.  Also, you want to do this all before the epoxy fully cures (cures in approx 24hrs)