Tim is right that it may not be popular with warehouse staff, but a Base UOM of bottles would work the best.
We have in the past used the Distribution Elementz module from www.gpelementz.com to get round the warehouse staff issue.
Distribution Elementz has various Inventory View windows that have the ability to switch the quantity views into different units of measure (based on each Inventory Item's specific options).
Just thought it was worth mentioning...
