I keep reading the title and then reflecting on the story. There are so many different ways to take it. "Inside" leads you to think about being "locked-up", as Sarge was sent to jail. But it also lends itself to suggesting the inner turmoil and degradation Sarge creates for himself through his experience.
And of course, the 'Welcome to Hell' reminds me of the many imaginings of hell writers have presented us with, the obvious one being Jail. Yet somehow, I think you really are refering to the 'hell' of a drug addiction and all the turmoil it causes for everyone involved (poor Kmack).
Again you've painted such a layered/deep picture.
Good job, and like the rest waiting for the next one.