'75 with some rot need advice

[195Pilot]

Just purchased a 1975 31 foot rear bath airstream. She had been sitting for a while, although in dry climate, Knew it was a fixer upper when I made the purchase. I took the rear down to the plywood and I have some rot in the floor no surprise, but there's not a lot and there is no separation issues yet.
To describe the rot starting left to right, at the battery box I have rot approx 6"x6" along the inner wall, at the rear, aft of the dump valves the plywood is rotten approx. 12" long .Then inboard under the toilet 12"x12" centered above the black tank. There is no rot 24" forward of the rear of the coach
My question to the experts is; Do I need to repair these small area's or go ahead and replace the last section of plywood.
I can not find where any of the bolts have pulled through. Im all for proper repair just need input as to which way to go.

thanks,
Jack

[TG Twinkie]

I say patch it and seal it. The new plywood will not be as good or thick as the old. If it ain't broke don't fix it

[Minno]

Ideally, if you patch it, try and put the seam on top of a framing member. You could also use a gusset underneath the seam, but that would not be practical over the black tank as it sits directly underneath the plywood. For small spots, others on the forums have used wood hardner and wood filler epoxy as a patch, and it seems to hold up ok based on their reports. I would avoid a seam directly under the toilet.

[Aage]

If you decide to use the wood hardener, I would remove the black tank and do it from both sides.

You want to be sure that part of the bad wood gets as solid as you can make it. Also, you need to make sure that the metal parts that hold up the tank (rails, pan) are not about to fall apart from sitting wet for years.

Of course it goes without saying that you absolutely must find and rectify the leaks that caused the damage in the first place.