Get 2 part expanding boat foam. 4lb. You mix it 50/50 and pour it in. It runs so make a water tight box is you're not just pouring it into a hole. It doesn't come out like a square, more like a baloon, so you can use visqueen plastic over the top to make it expand horiztonal to the pour hole. It makes a mess if it gets onto something you don't want it to. It's hard to clean off while wet. You can pressure wash it off the paint/glass once it is dry.
For resin, use marine epoxy. I use 3:1 as it's easier to work with. There are different ratios but 3:1 will work well for you.
For glass, use about 3 layers of 1208 biax. If it's going to be structural in anyway, or support impact, then you want to use something different. But, if you are just patching a foot hold hole, and only going to be pushing the side of your foot into the new glass, then 3 layers of 1208 will be fine.
I personally like to use extra layers of glass instead of filler. Example, I prefer to use 4 layers of glass, and sand into 4th layer (since I only needed 3) until it is smooth, then give it a protective coat of epoxy (don't leave exposed fibers. It's the tray, so it doesn't have to be finished. After that, simply scuff it up and put down turf. If it's going to be visible and paint it, you can use filler.
Edit: I said to use 4lb foam because 2lb foam shrinks more. I am assuming you are going to pour foam, sand smooth, then lay glass right over. The glass will stick to the foam, and the foam will pull the glass inwards as it shrinks leaving a large dimple. 4lb foam shrinks significantly less. For best results and least amount of shrinkage, allow the foam to rest for 24 hours after you pour to sand so it has time to do most of it's shrinking.
