These are purchased from the market, and come in various sizes to fit the different haulers.
You place the destination and price you are paying on the box, and fill it with whatever you like, and place it on the market or using a shipping menu interface.
Anyone can come to the outpost and ask to take the job, at which point they get a generic mission type cube of the appropriate size, and can take it to the destination and hand it in.
[science bit]
Each cube DOES NOT CONTAIN the items, just a bunch of complex quantum mechanics jiggery pokery, that allows the real cube to be teleported to the destination on completion of the job.
[/science bit]
What does this mean?
(1) People can place hauling assignments to get their stuff moved easily and safely by other people
(2) Multiple people can race to compete the exact same contract, only the first person to activate the device at the far end gets the reward.
(3) Cannonball Run style events across beta islands could be organised using the system and small containers.
(4) Your cargo can not be stolen by the person hauling it.
(5) Loosing the hauler does not mean the cargo is lost, so no griefing.
(6) People could use the system to 'insure' their own cargo by putting up and taking a hauling contract themselves, reducing the risks of beta hauling.
Now people might think it sucks, or that arguments 4,5,6 are too bad for a sandbox game and so don't want it or whatever, but perhaps something based off this could be added. The current system of 'large sell order here and large buy order there' is pretty inefficient market-wise, and places the risk entirely on the hauler, and there are no other mechanics in place (besides their existence) that recognise the importance of hauling in the game.