Sorry about that -- I forgot that the BA11 doesn't have those
bulkhead openings on the back door.
Let me guess -- the back door is just a solid piece of metal,
with a small adjustable slot towards the bottom, to allow
cables to pass through. . .
If that is the case, then what you would do is to obtain
one of the metal bulkhead frames that they use for
expansion on the q-bus & unibus boxes.
It's basically a rack-mountable metal piece,
with a bunch of bulkhead openings on it.
I don't know the DEC part number for that,
but someone with a DEC Systems & Options catalog
from say. . . 1986 . . . would be able to help you.