I have the exact same issue - saying it is caused by the undercoating. I dunno - I think the sensor should have a better seal on it to prevent this from happening. Will be getting car out of storage very soon - still undecided if I am going to fix it or just live with the light on. If I fix it, I will update with what it takes to fix.
**Update** Car is built, ETA for delivery to dealer May 22
Ordered April 6, 2011, 2012 5.0L, 6 Speed, 3:55, Lava Red, Satin Black Stripe, HID Headlamps with security package, GT Package #5. (Hood scoop, Pedistal Spoiler, Side Scoops, Rear Winow Louvers, Deck Panel)