Erosion of rubber fuel and hydraulic lines on older coaches

If the hose comes from the bottom of that tank, it is not pressurized.
I saw the same wear on my motorhome when I bought it, I did the same thing you did and wrapped and repositioned the hoses and clamps that hold the hoses in place.
My MH is 19 years old and doing fine.
If you are replacing the engine water hoses and want not to worry about them again, use turbo silicone hoses. They are a little expensive, but are heavy duty and won't deteriorate. Silicone hoses and gas and oil do not go good together tho.