Add weight every time something enters trigger

Hi! I have a project where you can play with three characters with several weights. The character ar NOT rigidbodies, thery have saved their weights in a variable in the player controller script. I want an object to be a trigger that breaks as soon as enough 'weight' is added. So every character can one by one be choosen as an active player and stand on this particular object, together they are heavy enough to break it. How can I write this for the trigger, to always add the specific weight that each character has if it enters the trigger? And in case, one character moves away before the trigger-object breaks, how to subtract it? Thanks a lot!