transom rebuild

[jobu]

If you leave three inches around perimeter...how do you get it in? (curious...planning a rebuild this off season).
I am a carpenter with a little glass expirience, I want to put on a bracket and fill in the transom. I am only apprehensive about doing the detail work like the baitwell and the edges and hatches. I will research this site further when the time comes...seems there is alot of good info on here.
But when it comes time to finisg the glass work...do you sand down and skim with filler to make it smooth?? (whats a quick discription of a good method)
thnx joe