defcon, This is the first time I have read any of your post . I'm assuming that you are a young person so I may sound a little annal. My first thought is this person even ready to carry a gun and second , why carry a gun in a back pack?
I have carried off and on for almost 50 years and never dreamed of carrying a gun in a pac unless it might be on camping trip or such. This week I'm using a Simply Rugged Pancake holster for my SP101. Last week I used the CrossBreed Super tuck.
For really deep concealment try the Smart Carry. If you feel the need to carry a concealed weapon I would suggest that you forget the back pack and get one of the many good concealment holsters.
Just my personal opine. Your mileage may vary.