This is why I utilize the method that I do. I run a pouch on the outside for the handgun, and have added a short bungee with a carabiner that attaches to a belt loop or belt to secure the bottom of the kit bag.
When I am doing things that I need extra retention I can just put the flap over the grip of the handgun.
Then when I am close to civilization/people where I don't want anyone to see the firearm, I can simply put it in the main zippered compartment.