Can you make the scrap variable instead of a fixed amount ? min & max value ?

Change this line:

Item item = ItemManager.Create(ItemManager.FindItemDefinition("scrap"), scrapCount, 0uL);​

'scrapCount' is what you want.
You can make a random function, like this:

Item item = ItemManager.Create(ItemManager.FindItemDefinition("scrap"), UnityEngine.Random.Range(1, scrapCount), 0uL);​

this will get a random number between '1' and configured in json (config).