The config has changed! See below to see how to modify your existing config

Changed some things around to avoid the error when restarting a server. The cause is still unknown
Fixed item amounts
Added config option for UI opacity

Config - Add 1 line shown below

C#:

{
  "LootTable": {
    "ContainerSkin": 0,
    "LootItems": [
      {
        "MaximumAmount": 100,
        "MinimumAmount": 10,
        "Shortname": "metal.refined"
      },
      {
        "MaximumAmount": 2,
        "MinimumAmount": 1,
        "Shortname": "explosive.timed"
      },
      {
        "MaximumAmount": 3,
        "MinimumAmount": 1,
        "Shortname": "grenade.f1"
      },
      {
        "MaximumAmount": 1,
        "MinimumAmount": 1,
        "Shortname": "supply.signal"
      },
      {
        "MaximumAmount": 1,
        "MinimumAmount": 1,
        "Shortname": "cctv.camera"
      },
      {
        "MaximumAmount": 1,
        "MinimumAmount": 1,
        "Shortname": "targeting.computer"
      },
      {
        "MaximumAmount": 60,
        "MinimumAmount": 20,
        "Shortname": "ammo.rifle"
      },
      {
        "MaximumAmount": 60,
        "MinimumAmount": 20,
        "Shortname": "ammo.pistol"
      }
    ],
    "MaximumItems": 4,
    "MinimumItems": 1
  },
  "Options": {
    "LootSpawnfile": "",
    "MinimumPlayersRequired": 1,
    "ShowSmokeOnLocation": true,
    "UISettings": {
      "IconUrl": "http://www.chaoscode.io/oxide/Images/treasureicon.png",
      "UIBackgroundColor": "#4C4C4C",
      "UIOpacity": 0.7, // << - Add this line here
      "UseUIDisplay": true,
      "XDimension": 0.275,
      "XPosition": 0.625,
      "YDimension": 0.05,
      "YPosition": 0.93
    },
    "UseSpawnsFromRandomSpawns": true
  },
  "Timers": {
    "MaximumTimeBetweenEvents": 1200,
    "MinimumTimeBetweenEvents": 600,
    "TimeToLoot": 300,
    "TimeToUnlock": 180
  }
}

The config has changed! See below for information regarding config modification!

Disabled chat commands when spawn requirements aren't met on startup
Added RandomSpawns support, by using this the spawnpoint will be a random point supplied by RandomSpawns and will not require a spawn file!
Added option to show a little UI display to show users the time remaining before unlock/despawn and the chests position

Config

C#:

{
  "LootTable": {
    "ContainerSkin": 0,
    "LootItems": [
      {
        "MaximumAmount": 100,
        "MinimumAmount": 10,
        "Shortname": "metal.refined"
      },
      {
        "MaximumAmount": 2,
        "MinimumAmount": 1,
        "Shortname": "explosive.timed"
      },
      {
        "MaximumAmount": 3,
        "MinimumAmount": 1,
        "Shortname": "grenade.f1"
      },
      {
        "MaximumAmount": 1,
        "MinimumAmount": 1,
        "Shortname": "supply.signal"
      },
      {
        "MaximumAmount": 1,
        "MinimumAmount": 1,
        "Shortname": "cctv.camera"
      },
      {
        "MaximumAmount": 1,
        "MinimumAmount": 1,
        "Shortname": "targeting.computer"
      },
      {
        "MaximumAmount": 60,
        "MinimumAmount": 20,
        "Shortname": "ammo.rifle"
      },
      {
        "MaximumAmount": 60,
        "MinimumAmount": 20,
        "Shortname": "ammo.pistol"
      }
    ],
    "MaximumItems": 4,
    "MinimumItems": 1
  },
  "Options": {
    "LootSpawnfile": "",
    "MinimumPlayersRequired": 1,
    "ShowSmokeOnLocation": true, // << - Be sure to add the comma shown here
    "UISettings": { // <<- Then add from this line here (9 lines)
      "IconUrl": "http://www.chaoscode.io/oxide/Images/treasureicon.png",
      "UIBackgroundColor": "#4C4C4C",
      "UseUIDisplay": true,
      "XDimension": 0.275,
      "XPosition": 0.625,
      "YDimension": 0.05,
      "YPosition": 0.93
    },
    "UseSpawnsFromRandomSpawns": true // << - To this line here
  },
  "Timers": {
    "MaximumTimeBetweenEvents": 1200,
    "MinimumTimeBetweenEvents": 600,
    "TimeToLoot": 300,
    "TimeToUnlock": 180
  }
}