I just dropped almost £600 on a gopro hero 5 and karma grip, and refused to pay the extra £180 for the magic gopro backpack.
This is my answer! Its a simple gopro mount that slips under the webbing you will find on the shoulder straps of most military style backpacks (like my trusty every day backpack). Designed for the karma grip, but there is no reason this can't carry any other gopro mountable object.
Print at super high infil if you value your camera, no supports necessary, and remember that the mount Is designed to be printed in something TOUGH. I used taluman alloy 910 which worked a treat.
Now get out there and film stuff!