inside your oxide folder is another folder called config, there will be a json called "LootTable.json".   Open that into a notepad or use notepad++ {recommend this program}.  Here you can add more lines to each "prefab".  Heli_crate is a prefab, bradley_crate is a prefab, etc,. 
 
You cant break the loot down into separate boxes (far as I know) when the heli or Bradley dies, it randomly spawns in "X" number of boxes (with "X" number of loot) and pulls the loot from the loot list.

"assets/prefabs/npc/patrol helicopter/heli_crate.prefab": {
      "Enabled": false,
      "ItemList": {
        "ammo.pistol": {
          "Max": 500,
          "Min": 200
        },
        "ammo.pistol.fire": {
          "Max": 500,
          "Min": 80
        },
        "ammo.pistol.hv": {
          "Max": 500,
          "Min": 60
        },
        "ammo.rifle": {
          "Max": 500,
          "Min": 120
        },
        "ammo.rifle.explosive": {
          "Max": 500,
          "Min": 30
        },
        "ammo.rifle.hv": {
          "Max": 500,
          "Min": 40
        },
        "ammo.rifle.incendiary": {
          "Max": 500,
          "Min": 60
        },
        "ammo.rocket.basic": {
          "Max": 3,
          "Min": 3
        },
        "ammo.rocket.fire": {
          "Max": 15,
          "Min": 5
        },
        "ammo.rocket.hv": {
          "Max": 5,
          "Min": 3
        },
        "ammo.shotgun": {
          "Max": 64,
          "Min": 8
        },
        "cctv.camera": {
          "Max": 1,
          "Min": 1

is an example of the heli loot you can add.  Here you can find the short.names and more for items:

https://www.corrosionhour.com/rust-item-list/

The plugin does'nt support this. Deactivate both types inside BetterLoot and use another plugin for those types.

Example for heli is: HeliControl