You've probably seen my big metal boxes on DayGlo Avenger and CrazyBike2, but they are made from old rackmount test equipment boxes. The ones I use now are aluminum, but there are steel cases taht coudl be used too. They're pretty tough; I did bend one up some when I clipped a vertical post on an underpass railing with it's front edge at speed (instantly stopped me, just about), but it didn't break or tear open, or come off the bike.
You can get cases like these at many electronics salvage yards, or buy up really old server cases off ebay, or whatever. Same thing with old test equpiment (some of which can just slide right out the front, so you can still use the test equipment without the case, if you like). Some places just throw this stuff away, so you might get it for nothing.
They're pretty big--compared to a shopping cart, for instance:
The lockable lids are the tops off of rackmount server cases, using the case / system locks from different PC cases. (ideally I'd use a pile of old IBM AT-case locks I have, but I don't have keys for any of them.
) The lids are attached via piano-hinge salvaged from seat/compartments discarded from someone's van conversion, IIRC. (the old lid hinges were just cabinet hinges).
They're large enough to contain an entire 30lb bag of dog food and still close the lid; a 40lb bag will fit almost completely inside. There is a lot less room when i use the styrofoam liners in them to keep things cold or hot (and to reduce echoey noise); the styrofoam is repurposed insulation from the fish and plant and reptile shipping containers we receive at work each week, which would otherwise be discarded. So as it wears out from use (flaking away) I have a never-ending supply of new liners.
They're also large enough to carry a seated 40lb+ dog.
Or a whole bunch of assorted stuff, when the rest of the bike configuration allows it:
With them mounted high enough so the tops are level with or above the rear tire, I can also use them as a wide cargo rack that can hold up at least 80-100lbs, although this doesn't make it very easy to maneuver--much better to have that weight *in* the boxes than on top of them, whenever possible. But they *are* handy for putting another box across to contain more groceries when shopping, so I can fill up the two boxes with heavy and/or cold stuff, and put the lighter and unregulated-temperature stuff in the box on top. Easier to deal iwth in traffic than a trailer.
Just regular grocery shopping:
This is how I built the one on DayGlo Avenger
http://electricle.blogspot.com/2008/12/ ... -some.html
which is featured in the pic above with Hachi in it. I dont' recommend the rivet method shown; it won't hold a lot of weight and they'll break from vibration (and they weaken your stays). But you can do what I did later on and cut slots on either side of the line drawn in one of those pics, and use hose clamps thru them and around the stays to secure everything--that works pretty well, if you use enough of them in the right spots on both seatstay and chainstay.
They'll work a lot better if you build a proper sturdy mount for them that is securely bolted to the frame, but they will work with the clamps for lighter loads--just don't go hauling big bags of dog food, or big dogs, in or on them with just the clamps.
Over time the clamps will tear thru and bad stuff happens.
Somewhere on my Electricle blog, there are also posts about using kitty litter buckets for pods, whcih is what I used for non-basket applications before the metal boxes. They're water-tight, fairly tough, and lockable if you use something like a shed-door hasp and padlock. on each side of the lid (or a cabinet hinge on one side and padlock/hasp on the other). But the plastic rots pretty quick in the Arizona sun, so you have to paint htem, and even sanded down paint doesn't stick well to the knds of plastic they are usually made of. Either way, the Tidy Cat red/yellow or blue/yellow buckets are the best ones for the application. All the others are flimsier than the TC buckets, by quite a bit, and crack much more easily.
Steel ammocans can work, too, but so far I've only used those for battery boxes. 50-cal cans are the largest I've had in my hands, but Iv'e seen bigger ones. They're also all water-tight, and quite tough. Below shows the white ammocan under/to the side of the seat, just forward fo the metal cargo pod. I oculd probably put three or four of those ammocans inside the pod, volume-wise, and at least two actually would fit in there with room around htem both.
I have yet to make the support frame for them and use them in practice, but big bags like these computer-case carrying bags (salvaged when CompUSA shut down a few years back) can also work. If you already have an Xtracycle or similar, you could just strap them right on. I expect there are bags similar enough to these still avaialble as luggage carriers that you could find something nowadays. One of the metal cargo pods is in the pic to the top right for size comparison.
Frame will be made from these old aluminum cots:
Something else I've used is the big ABS battery boxes from powerchairs: Some of those use two car-battery-sized SLAs that slide onto a rack behind the seat. So the boxes are just bigger than a car battery, and fairly tough. If you mount them using the part designed for that, they'd probably last forever. You'd basically use a rectangular ring around the top (like the top edge of a regular bike basket) to hang them from, letting the bottom rest against or be bolted to the side of the bike. But don't mount htem using a plate on the inside to spread the load, becuase they'll just rip at the corners instead.
Especially on bad roads with no suspension and heavy loads in them.
Pic below shows one used as the 48V20Ah Vpower pack battery box at Death Race 2011.
A trailer is naturally another option for cargo, but I can fit so much in the pods that normally I don't need to use the trailer--it's just easier or lets me haul bigger stuff, or use them plus the trailer for lots of stuff at once.
And if need be, the sides come off the boxes for stuff that won't fit in them width-wise:
and could then be tied down with paracord or bungees. I've done this a few times, once with a microwave oven and another time with a chair.