It sounds like you are on your way!

See what Jerry has done on his commander for reference... Some lovely work there - you should follow his lead. And maybe you'll want to incorporate the mast base in your repair as he did... That is a great idea.
http://www.pearsonariel.org/discussi...1672#post21672

Cut a circle big enough to get to good-solid material... Since you already have a failure I would expect that the area will be the 8" circle (mast base), plus at least 2-3 inches around the perimeter which has suffered deformation. Make that whole area solid... Much less than a gallon!

I would not use pure epoxy. Use a bit of thickener and some glass mat on you repair. Jerry posted a good description of the process a few post above here...