Foggy makes some excellent points. Unfortunately there are few, if any surveyors who can really determine the condition of a C D Dory (the "raw" older 22's without a cockpit non removable floor were probably the easiest to "diagnose ) . I don't have a lot of faith in the run of the mill SAMS marine surveyor.
Osmotic blistering is very rare in the C Dory line. I have seen some gelcoat blistering in several of the green strip and bottom older C Dorys.
The 25 (and the Tom Cat, plus Ventures) are the hardest to ascertain the condition. The 25's have the cockpit floor over the fluel tank, and multiple screws into cored cockpit flooring. There is a "grid" holding the 100 gallon fuel tank in place, and there were some sort of spacers holding the tank off the inner hull. These spacers seem to degrade with time, and leaves the aluminum fuel tank sitting is water--often salt.
The proper way to build any cored boat, is to put solid, non water penetrable in the way where screws are placed into a "cored" structure. This would include solid fiberglass Laminate, Coosa Board, PVC "lumber',
Builders like Hinkley do this. But compare the cost of a Hinkley to a comparable sized Hunter or Catalina! In other words, you have to pay a lot more, and selling boats is a competitive business. Plus most buyers just don't care, or more likely don't know.
Some 25's have the tabbing from the inner skin of the hull to the aft cabin bulkhead, come loose. From what I can tell, C Dory has only used one layer of mat or 6 oz cloth. To do it properly, when it has broken down, means cutting out the floor (even those with hatches, have to cut out a little of the deck, to get adequate clearance to pull the tank. Then the bottom of the boat (inner skin) has to be cleaned and assessed. The core of the bottom of the boat examined both physically,, by percussion and by moisture meter (after all water has been removed and the boat allowed to dry out. The repair is to place concentric layers of tape such as 1708 laminated with epoxy. That is "bullett proof." and should last the life time of the boat. The average boat does not have this problem. But if there is "unknown'" source of water inside the cabin floor, this is most likely to be from this tabbing delimitation. If the core is compromised then it should be replaced at this time, the fuel tank inspected--if the boat is over 15 years old, consider a new tank, Which will be coal tar epoxy coated, after proper prep. The tank should be spaced so that air (and water) can flow freely under the tank. I would also put one of the mini pumps which pull all of the water out of bilge just in front of the fuel tank, and make a plate to access it down the line. This should keep water from accumulating there in the future.
Boats that have floors, where you cannot access the inner side of the bottom, are harder to know what is going on there. There should not be any screws penetrating the core. However if a fuel tank leaks, and ethanol gets onto the fiberglass, it can destroy the polyester resin, and open the laminate to water intrusion without a screw penetrating the hull.