As Bruce mentioned, I have seen the trailer he restored. I did get the opportunity to inspect the trailer in detail including the roof.. Which is free of blemishes, bumps, wrinkles, crevices or any sort of distortion to a completely smooth surface.
In looking at the photos Bruce provided a link to of the restore process I am struck by the variance in the type of substrate that is on Bruce's trailer versus what is on other RV's.
While Bruce did not replace the entire substrate he did replace what was damaged. I am thinking he replaced the entire sheet if any portion was damaged.
As has already been pointed out there is a requirement for a smooth clean surface. In some instances it may be necessary to replace the entire substrate, or the most economical alternative.
What this boils down to is that for those that do not have the experience or knowledge or skill set to take on the task of replacing a roof covering then one has to rely on whom they chose to accomplice the repair.
As an aside we have had an instance where a manufacturer shipped a class A where the roof had not been sufficiently cleaned prior to the roof covering being applied it was laced with bumps and blemishes. The manufacturer after some persuasion brought the coach back to the factory and replaced the entire roof since whatever substrate they used could not be sufficiently cleaned and repaired.
Having seen many of the projects, and repairs that have come out of Bruce's shop his reference to him being an amateur is akin to Moby Dick referring to himself as a minnow.
JohnnyT