Ted, six months (180 days, 360 packets) is going to be a bit of work no matter how you do it. The only way I can think of doing this, without having to open/close/reseal things and pack lot of bottles, would be to get a home sealer and make up daily packets.
The vacuum sealers would be the best bet, you can literally make up small sealed pouches for each set of pills, making up packets and then cross-sealing them and cutting them apart (or keeping them in strips), and the vacuum bag material is much better at keeping air and moisture out than ziplock bags are.
A bit of a production to get it all done...but unless your pharmacist has any other ideas, I think this is the way to go. And of course, you'll have the vacuum bag machine available for other purposes.<G>
Maybe it would be enough to vacuum bag "one week" of each, with one of the dessicant packs, and then do a weekly transfer of the pills (and the fresh dessicant pack) into a small Pelican or Otter Box to keep them "waterproof" and dry enough for each week as it goes?
Bear in mind, if there's an oven
or burners onboard, you can rejuvenate the desiccant packs, too.