Air pin boxes are a waste of money on a heavy trailer.
Why?
I always ask the owner when I see one -how much PSI are you running?-
because at around 80-90 # they are practically a solid, vibration damper at that point.
They have too little volume and surface area,Air hitches are a better solution but quite heavy , the E.T is 700 pounds,
They are a wonderful hitch if you can swing it ,my trailer no longer swung up and down in a 'teeder totter' motion but now moves in a horizontal plane ,alway on a level .
It also can be used as a aid to unhitch,pull pins on landing gear and make contact with the ground ,air out unlock and drive out.
Reminds me onboard air is another expense .
good luck