As Outdoor_quest mentioned, Oregon Packworks sounds like it's just what you asked about. I know a couple of hunters who have raved about it.

Anything that customizable will be heavier, obviously. What also adds weight to Packworks is the ability to carry a heavy load. Not as handy backpacking, but for hunting and especially a bug out bag where you might want to salvage something heavy, it's nice to be able to carry 100lbs a short distance.

J