Does anyone know the link to print out the customs form?  How much extra is it to send a book this way?

Hi Kelli, it will not cost you anything extra send a book to an APO, the only extra requirement is that you have to take them to the counter at the PO, you cannot just drop them in a box anywhere even if you use the online form and online postage.

The online form is located here Customs Form 2976-A. I find the handwritten form easier to deal with so I just get a couple extra to have on hand at home.

There are actually 2 different forms that you may have to fill out for international packages, and APO's are classified this way even thoug you pay domestic postage on them.  The small one with the green tag on it is for packages weighing less than 1 lb., and the white (5 page pressure sensitive one) one is for p[ackages weighing >1 lb.  You can print them on line but you can get several copies from the clerk as soon as you go to the PO the next time.  I keep a few of both in the drawer in my desk.  (You don't have to fill out 2 forms, just one for a package depending on its weight.) 

The reason it does not cost extra to mail to the APO is because you are only paying for the package to get to a military facility within the US, then the military is responsible for the package from that point on.  Some interesting info about APOs:

The USPS has formalized a standard addressing scheme for all domestic mail. Many will of course recognize this as: 

In order to make Military Mail conform to this scheme, several things were created. These were:

Three Military "States":

AA, which stands for Armed Forces (the) Americas
AE, which stands for Armed Forces Europe
AP, which stands for Armed Forces Pacific

Two "City" equivalents:

APO, which stands for Army Post Office
FPO, which stands for Fleet Post Office

Based on these constructs, a typical Overseas Military Mail address looks like this:

By having all Overseas Military Mail conform to the domestic mailing addressing scheme, the USPS could easily sort and manage it using their sophisticated sorting and distribution machines, just like regular mail.

But there is more to these constructs than addressing schemes. The Military State designators mean more than "phantom" states. They represent the USPS mail processing facilities that handle the mail traffic to and from each Military State. In an analogous form, they represent the neck part of an hourglass. Picture mail flowing into a "neck" location from all parts of the continental United States, then from this "neck" out to all the Military bases and U.S. Embassies in the region of the world represented by the specific Military State.

These "neck" locations, the USPS mail processing facilities themselves, are located in cities that are conducive to getting mail to and from the overseas region of the respective Military State. These Military State/City pairs are:

AA : Miami, FL
AE : New York, NY
AP : San Francisco. CA

Since these cities already had ZIP codes assigned to them, it was decided to have the ZIP codes of the respective Military State be numerically close to the ZIP code of the city where the mail processing facility is located. This allowed the USPS automated sorting equipment to funnel the Military Mail to the proper city where the respective mail processing facility is located.

Once the Military Mail arrives at the respective mail processing facility, it is further sorted by Postal Service Center, APO/FPO and ZIP code. After that, the USPS "hands it off" to their Military equivalent in a branch of the Armed Forces after transport via contract air carrier and delivery to the overseas APOs and FPOs. For APOs, either the Army or Air Force provides personnel. For FPOs, the Navy does the job.

If I print out the customs for at home and use DC/Postage through PBS do I still have to go to the post office?

Yes, you still have to go to the post office.

Any package going to a military address overseas, must be mailed from a post office, due to customs regulations.

Letters can be put in your mailbox or the blue box, packages cannot.

Good luck!

Leigh