From my understanding, neutral and ground are only supposed to be
bonded together in one location: the main service entrance breaker box.
If I am bonding neutral to ground at this second location (my meter
housing), isn't that bad?

Yes bonding the neutral and ground at a second location is bad and it
violates NEC. If you do bond them here you will split the neutral
current across the neutral conductor and the ground conductor. The
ground conductor should not have current on it during normal operation.
You must find a way to isolate them. What exactly are you trying to
meter?