Many thanks to
@Prf_Moriarty for the use of his awesome convent scan!
Car Paint settings used (under water): Specular Weight 0.2, Specular Roughness 0.2. Scene tutorial here.
Thin Walled with SSS. Diffuse Ray Depth 4. More examples here.
How to use ooOcean in the viewport and with Arnold.Available for free :