How to handle "Recurring" Purchase Orders? e.g., vendor agreements

How are companies handling the scenario in which there are recurring Purchase Orders such as vendor agreements? 

Example - service agreement with the vendor to perform $1,000 of maintenance service each month. 

My thought is that this is handled through Blanket POs, but looking for input from others! Here’s what I did. 

• created blanket PO with 1 line item but qty. of 3 (representing 3 months)
  • also set expiration (3 months in this case)
• create new PO - normal type
  • added PO line item from blanket PO - adjusted qty. to 1
    • remove hold/approve (Normal “child” PO = Open)
• Blanket PO = Open (because there is still open qty. of 2)
  • Qty. on receipts = 1

Are there any other ideas or methods? What are others doing?