Wouldn’t it be easier to attach two Collision components(box) to the Camera component. These invisible walls will always follow the camera. To position them accordingly to Viewport size just Get Viewport Size node / 2 = X. One wall will be at Camera location(x-axis) - X and the other Camera Location(x-axis) + X. Maybe I’ll test it out later for you.
You could set these walls to only block the players and nothing else.
Oh I was thinking of a 2d side scroller, my bad 
Well I think It could still work though you would add two more walls on the y axis.