I know about collision enter, collide, stuff like that, but is there some way to constantly check if there is any rigidbody within the trigger at any given time? The only way for the trigger not to fire is if absolutely nothing is inside of it.
No, you have to code that logic yourself by keeping track of what has entered/exited the trigger
Oh so it should be as easy as adding one every enter and subtracting one every leave?
It should be, yes