Well if I'm interpreting this correctly, with the world being a crapsack... Military personel in universes like this are usually people signing up for service to escape a life of poverty. People willing to put their lives on the line for a few extra dollars (military grunts arent paid that well), are probably also willing to accept a few bribes, especially if provided with a plausible and non disasterous reason.

So, you could try to sneak onto a ship by bribing a guard, saying that you're a lover/friend of one of the men serving on it. Don't tell him you'll steal the ship, but for someone in poverty, a few credits would probably be worth looking the other way to let his squad-mate get some action.

Granted, our characters aren't exactly rich either, but provided we could get a bit of money, that would be an option.