plural forms - "Number" or "numbers"?

Is there a difference between using "number" and "numbers" when referring to multiple numbers?

For example, when calling a merchant to inquire about multiple orders, should I say:

I need RMAs for order numbers 1 and 2.

or

I need RMAs for order number 1 and 2.

This question might sound stupid, but I'm not sure what the main subject is. Is "number" the subject and therefore should I use "numbers"? Or are the order numbers (1 and 2) the subject, so should I keep "number" singular?

Answer

I usually hear that as "Order numbers 1 and 2", with the "s". Fumble's comment gives a good way to get around it anyway.