Hi and welcome aboard. Like Phatdaddy said, if it were me I'd go the Seacast or Arjay pourable transom repair. Unless you're used to working with wood (I'm not) it seems to be the best and easiest way to fix the transom. In a few words, you take off the top covering between the two fiberglass skins (Inner and outer) remove all the wood (good and rotten) and pour a liquid into the void that will harden into a solid permanent repair. There are several posts on this site from people that have used this style of repair to great success. Just do a search. And remember, we love boat porn here, so be sure to post any pics of your boat and it's repair or just pics in general of you and your boating pleasures. 
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1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
If God didn't have a purpose for us we wouldn't be here, so
Live simply, Love generously, Care deeply, Speak kindly.
(Leave the rest to God) 
Silence, in the face of evil, is itself evil. Not to speak is to speak, not to act is to act. God will not hold us guiltless.
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