I had seen the start of plastic distortion/melting, and I had noticed that the passenger side was noticably hotter than the driver's side, even after adding high-flow cats.
After looking all around to define the problem it ended up being that the glue buttons that held the side sill insulator and popped loose, and the insulation was shifting down withing the side sills, leaving the top open to the heat.
After figuring that out, we fed the insulation inbetween the body and exhaust first, making sure that it was tucked in before putting the cover back on. It made a HUGE difference with the side sill plastic cover just warm to the touch, rather than blazing hot as it was before.
I'd have the dealer check it out for you before it melts further, or perhaps starts a fire.
-Dean.