There is a chemical; like a paint on material that will harden and strengthen dry rotted wood to be stronger than it was. I cant remember the name of it but, it is used in the boating industry to repair wooden boats. You may be able to get by for a while with that. Also I've had some success using fiberglass resin. I just mix the resin and hardener and saturate the wood with it. and let it dry. I made a repair on my cab over using this method and it's held up well to this point. I must say though it wasn't in a structurally important area like you discussing here.