{
  "ArmorRate": 1.0,
  "CheckAuth": true,
  "DecayArmor": true,
  "DecayMetal": true,
  "DecayStone": true,
  "DecayTwig": true,
  "DecayWood": false,
  "EntityRadius": 30.0,
  "MetalRate": 1.0,
  "NeverDecay": [
    "RHIB",
    "Rowboat",
    "HotAirBalloon",
    "minicopter.entity",
    "scraptransporthelicopter"
  ],
  "StoneRate": 1.0,
  "TwigRate": 1.0,
  "WoodRate": 1.0
}​

The scraptransporthelicopter is decaying (it is in the field of the tc).

I don't use any other plugin used for decay or similar.

edit: Should be ScrapTransportHelicopter and not scraptransporthelicopter...