Dry rot - wood underneath was soft and crumbly, like eaten by termites - but it is a fungus, as result of water leak. Such damage is often inconspicuous until it's final stages.
- recaulk the cracks, check roof marker lights often
- replace plastic roof vents with metal ones
- windows, especially front overhang window on class C are major source of water leaks.
- look for irregularities around window and door frames
- screws that won't stay tight you may have a problem. If the screws are rusted or corroded you DO have a problem and it's a good indication of dry rot
- A day or two after you've washed your RV or after a rain storm check along the bottom edges. If it is still wet you probably have a leak. Check it out.
- On the inside, look for water marks on the ceiling especially around roof vents. Remove the vent flanges and air conditioner shrouds and look for discoloration in the wood. That's a sure sign of a leak and possible dry rot.
- And, of course, check around the windows. Look for discoloration, softness of the paneling and loose screws.
- Repairing the leak - but that is only part of the repair. You must make sure the wood is dry. If there is any sign of dry rot treat the wood with an antifungal solution: regular household bleach, or commercial formulas
- If the wood has decomposed enough that the screws won't hold, don't just put in longer screws! Git Rot, an epoxy like product, can rebuild dry rotted wood, but if you wait until the long screws won't hold there may not be enough wood left to rebuild.
- Wood stabilizer to fix even separated plywood.
- Antifreeze/borate treatment from boat builders
- Putty tape to seal out moisture. Butyl tape ONLY on roof. Cheap is easier to handle.
- In warm or hot weather the tape may stick to the backing material. Chill the roll in the fridge.
- apply the tape to the object, not to the rig. Example: Putty tape the flanges of a roof vent, working the tape down firmly on the flanges before removing the backing paper This will eliminate waste, properly locate the tape itself, and get the backing paper off without a big mess.
- Apply to rig: to smooth over "valleys" with small pieces, then cover with single top layer, see link above.
- Eternabond tape - 4" wide is simpler to handle than 6" wide. 4"x50' for $50 at bigrocksupply.com
- cut some 2" squares and apply to the roof where the antenna "feet" make contact to prevent from wearing through the rubber roof.
- Eternabond sticks strongly and is impossible to remove: must be placed in its exact and final location on the first try. Put it into the freezer for about half an hour prior to use, so it will be less sticky and easier to use.
- Waterproofing Repair Tape sticks even underwater.