Not Difficult, But Time-Consuming
Depending on just how extensive the rot is, it could be a major effort. Consult extensively with the surveyor. Only you can answer if your up for it. The material is not that expensive, but your time commitment will be. If it was me I would consider the worth of the boat relative to the project. There are other boats out there, OD27's included that will be in better condition. If you are really set on this one, use it to your advantage and low-ball her. You may want to research the cure before you decide. You have time, don't rush into it, I'll bet there not lineing up to buy her. Get Don Caseys "Fiberglass Hull and Deck Repair" book, scour the web for information...its out there. Speak to fiberglass and epoxy suppliers for leads and tips. West Systems epoxy has good info on these type of repairs.I have found both balsa and plywood on my OD25. Depends where on the deck the rot is. Either material calls for removal of the deckskin, removal and replacemement of the rot and replacement and blending in the deckskin. Its fussy, and time consuming work, but quite doable for the DIY'er on a small scale. Good luck with your decision.Don