Even an additional cost of a few cents per package would work out to huge numbers for the kinds of scales that UPS or FedEx deals with. This certainly wont be just a few cents, either. For a device that'll get a decent GPS signal inside of a package in a big metal truck, be able to upload its fix to an onboard or remote computer, and last for at least 5 days . . . you're talking big bucks. Much more feasible would be to simply interface with the truck's GPS.