Create an Interface with a Crafting Upgrade in it. Then, specify the items that you want to keep in stock. The items will now be autocrafted if needed.

To make the stocked items available to your storage network, create an External Storage and put it on the Interface.

Make sure the External Storage is in "extract-only" mode. That way, Refined Storage won’t attempt to insert items in the Interface that is meant for keeping in stock.