Recommendations for managing demo units

We send demo units to customers (we call them consignments) for a set period. If the customer wants after testing, they can purchase these units; otherwise, they need to return the units to us.

We need the ability to do the following:

1. Track the customers who have demo units

2. Track the demo periods and when the units should be returned

3. Charge the customer for the demos should they decide to purchase them

Currently a zero sales order is created for a demo unit and someone needs to remember that the unit has been sent and when the customer should be returning it.  Need to automate the process.