I like the train idea. Though I feel like the most logical way for it to happen wouldn't exactly be exciting D:
I mean, logically, on the ride each hybrid would have their own cage, and they'd be taken care of. These are expensive soldiers. Why would they allow them to die, or nearly die of hunger or thirst? And, even if they nearly die but survive, they'd be too weak to hunt or find sustenance when they're released, and thus would die anyways. It would be illogical. The scientists are indifferent when it comes to "improving" the hybrids, thus the testing, but needless harm while they're merely sitting around? No, that would be a waste.
And allowing them to be free amongst other hybrids isn't the best idea xD They'd probably mutiny and find a way out, and the scientists can't have that. So they would each have their own cage, probably with a good number of other caged hybrids in one of the cars. And considering that this lab is a PART of the government, then everything would be good quality, so this cattle car stuff wouldn't happen xD The cars would probably be modern, strong shiny metal and whatnot OwO Let's see, the cages inside would look like.... hm.. -rummages through Google-

Imagine this, except human-sized and hybrid-strong. They would be essentially put into rows, making up both walls. Here, have another picture.

(Put in the cages from above in place of these cages) Except, naturally, the car would be somewhat narrower, and a heckuva lot shorter xD