Make it a family, office, or Scout project!
And don't worry, the troops prefer melted chocolate to NO chocolate!
Candy is quite heavy, so in this case if often pays to use the FLAT RATE Priority Mail boxes. You pay one price regardless of weight. (about $8 to $10 a box). Get some boxes first from the post office and compare costs. There's really no hurry now so if parcel post works out cheaper use that. It will depend on how much you mail. The USPS offers a $2 discount on some Priority Mail boxes to Army Post Offices (APO) so make sure you get the right ones!
Another option: separate the candy and use any non-Halloween looking treats to fill up some Christmas stockings for the troops! These should be mailed by Thanksgiving.
Whenever you send something, be sure to let the troops know you received their name from "Aunt Nancy" at "Aunt Nancy USA".
Email me at email@example.com and I'll tell you were to send it!
Be sure to include a note with your name and address, indicating you have checked the candy. No homebaked nor homemade food should be sent. Store bought only, in original packaging.