Man, this is an outstanding idea.
Sign me up for round two (I plan to have 100 posts, and will have some member feedback by then)
To clarify, USPS considers APO and FPO addresses domestic shipping, which means you're paying for a domestic rate. This include flat rate boxes, if you're not shipping flat rate, you're paying to the APO hub, for example, all pacific APOs (Korea, Japan, Hawaii) the hub is in California, so you're actually paying shipping to california, and the army takes it the rest of the way. However, if the package is destined for another country, even though you're paying domestic shipping, you will be required to fill out a brief customs form (it's literally your name and address, the destination address, plus what it is "Keypad" and value "$30" and that's it) I would suggest asking for the customs form when you walk in, and fill it out while you're waiting in line. They then have to punch everything you wrote on that card, into the computer, so you'll be waiting another like 2 minutes because post office workers never seem to know how to type. And then you're out.
TL:DR - Sending mail to an APO is exactly the same except you have to spend 30 seconds filling out a customs form, and stand there for two minutes watching staff fumble around a keyboard.
Now, the major problem is, depending on which post you're on, you're looking at anywhere between an extra 5 and 10 days in shipping time. Since you're shipping it to california, and the army goes and picks it up, puts it on an army plane, and flies it out to me, it takes a little longer. The army cares, but only cares so much.
So, that being said, I'd love to sign up for round to, but I'm happy signing up for the last spot (I might just be in the states by then anyways)