From our experience RUBS is like putting a bandage on something that needs stitches and hoping it solves the problem.
What you are doing essentially is splitting the bills x many ways. The problem is, when there is a leak and that bill goes up everyone is paying more and everyone becomes unsatisfied. Seen alot of parks go under from RUBS
I say sub-meter and charge the tenants for what they use. Keep it fair and keep everyone happy. Monitor usage, find leaks and problem tenants instantly.
Our system reports everyday so not only will you be able to bill back for actual usage you a can pin point issues proactively.
Most people who factor the Meter install in the cap x get there money back in less than 2 years in most cases.
Let me know what you end up doing!