The chipboard in many of our coaches, and to a certain extent, plywood, tends to just disapate when wetted repeatedly. So by the time it is discoved, a 3/4" piece of material may be 3/8" thick in spots.
It is my feeling - no test results, just feeling - that Rot Doctor is able to restore something very close to the strength the wood had originally, considering the amount of material remaining. So a piece of chipboard that is now only, say, generally 1/2" thick is not going to be as solid and strong as the original 3/4" material around the affected area. But it may very well be nearly as strong as new 1/2" material.
I have been really impressed with Rot Doctor.