Roof

A buddy of mine was telling me about his 1992 motorhome he bought last year. The roof had a leak so the previous owner fixed the leak then had that spray on bedliner (like the bed of a truck) sprayed onto the roof. Anyone hear or think of this before? Claims it was dirt cheap compared to a new roof and should last a long time. One problem I first thought was he sprayed it over the original rubber roof so it "floats". Not sure if removing the roof and applying the spray liner would be better.