If you let the boat dry between uses, rot should never be a problem. If you do have any trouble or you're really concerned about future problems, you can treat the inside of the boat with ethylene glycol - aka. antifreeze. Pour some into the boat and slosh it around until the entire skin and frame is coated. A garden sprayer might be useful for getting into some areas. Pour the excess out (into a container, so you can re-use it) and allow everything to dry. E.G. will kill existing rot fungus and help prevent new rot from starting. This treatment can be repeated annually or whenever you think you need it.