Yes we ship to APO and FPO addresses! The customs form will generate on the label based on the data associated with the package. There are no extra steps - you just need to purchase the label and you are good to go.
If you get an "invalid address" error when trying to ship to an APO address go into the order's information and check their address. If the state says anything other than "AA", "AP", or "AE" then you won't be able to purchase the label!