i used truck bed liner coating on the inside of my car. real tough stuff. and easy to apply. it was around 100 bucks for the kit. it comes with the gun to spray it. it s called raptor-something or other.(i can look at the box if u r interested). i only used half of the kit. i still have the other half for wheel wells, and other stuff. best undercoat style material i ve ever used. you gotta watch some undercoats/ they might say black but some are a brownish color and look like poop. 3M also makes a nice undercoat too.
