Professional modder....thats funny. No I work in a fiberglass shop.
gjmsd We use polyester resin, because it is much cheaper. For the amount of product you would ahve to use for a transom, it would cost a small fortune for the epoxy. I can get a 55 gal drum of polyester resin for about $1000. I can get about 3 gallons of epoxy for about $250-$300. Most transoms would take about 6-8 gallons. I can do many more transoms with the polyester than I could with the epoxy. Now having said that the epoxy will usually stick better with out much preperation, and epoxy is usually a bit stronger. But the cost just does not make it woth it.
I think your ratio is off. I would not put that much powder or microspheres in it. The microspheres do not have as much strength as the chopped strands. If your batch is too runny, then add more chopped strand.
Dave inGA yes you want to add about 1 gallon of chopped strands to each gallon of resin, now mind you the gallon size ziploc bag is just an estimate. You want the mix thick, and not dripping with resin. If you still have a bunch of resin dripping from your stir stick when you bring it out, then add more chopped strand. If you can bring the stir stick out with a bit of the material on the stick and it does not immediately drip (with in a couple seconds) then youe have it just about right.