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 :
Very honored to be a part of www.avantform.com
Rendered with Randomwalk v2 SSS. High resolution images here.