Thanks for your responses and inputs. Much appreciated.
I tried carry in a maxpedition monsoon. The idea of off body carry was too unnerving for me. I can't logistically keep it on my shoulder all day but putting it down (within my sight) means me losing my immediate control of my gun. Bad ju ju.
i have a Camelbak Demon backpack (two shoulder straps) which has a separate gun compartment at the bottom, which is accessed through a velcroed opening which sits against the back when you're wearing the pack. i also have a single strap Messenger Bag by Blackhawk, which also has a dedicated gun pocket, and a Maxpedition Jumbo bag with a dedicated gun pocket.
as other posters have said, however, you should maintain possession and control of the bag at all times, and there is no way to disguise the weight of the gun/ammo/reloads that you're carrying.
I have a Targus laptop backpack I carry my everyday stuff in. The laptop compartment is padded and I stash my gun in there at times. Not Maxpedition quality but holding up well after a year.
Why would someone be looking in your bag? My first thought was about baseball games, concerts, or gun shows. At those venues, they usually check backpacks looking for prohibited items like firearms &/or foodstuffs or drugs.
I, too, would be uncomfortable carrying off-body. I can't count the number of times colleagues have left briefcases behind that could well have contained a firearm. I would be too worried about losing control of my firearm by setting a bag on the floor or on a table.