"The tradeoff could be price and weight and I wouldn't be surprised if the barrel harnesses currently on the market fit these as well"



Voyageur Barrel Harness - from Ostrum
[K0047] $199.95

they have a couple of others for about $130, but might be too small for a big box ?
 

I wouldn't waste my money on a barrel harness to adapt, when you can likely find an old packframe at a thrift store for $10 - an hours work with a piece of plywood or something would make a shelf for the box to sit on and a couple of straps for quick on or off - about what I have rigged on my packframes for carrying the boat if I want to strap a pack on instead.  or just buy a freighter frame packframe like this  for $65 - likely cheaper than buying seperate straps and hipbelts and adapting

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used to work for an outfitter that used those Action Packers a lot - they held up to a lot of abuse, but sitting on them eventually "sprung" the top seal, so I wouldn't recommend useing them as chairs - they did fit tightly when shoved under a thwart, and fit crosswise in most canoes.  He'd bring maybe a dozen or so - it was "fun" to try and find what you were looking for without having to go thru a dozen boxes before you found it. worked well to keep bread and chips from getting all squashed.