Anonymous wrote: Secondly, the easiest thing to prevent bulging of the bins is to drill two sets of holes 1 foot and 3 feet off the ground in each of the lateral (long side) of the plywood and thread it with ~ 4.4 foot threaded rod (1/2"). Put a thick fender washer on each side and screw them down from either side of the two pieces of plywood (total of 4 nuts needed). This will give enough support to prevent bulging out from the weight of the coal within.
That's a good idea too, you could use eyebolts and a cable to accomplish the same thing. Even eyebolts and cheap set of ratchet straps. Ratchet straps may even be a better idea because they can easily be removed.
Three things I did forget to mention, first is leave access to the top of the bin if you put a roof on it, whether you put the roof on hinges or make it completely removable. Even if only half of it is accessible or has a small opening in the top. This applies to any bin, easy access to the highest point of the bin makes my job very easy. I can put coal nearly anywhere but I can't put it through walls.

How you set your bin up can mean the difference between 10 minutes or an hour, I have even refused future service to customers unless they were going to modify their setup simply because they made it too hard. I don't mind working but I'm not going to kill myself to make a delivery.
The second is if your going to do any reinforcing the bottom is the best place to do it. In the "short" 15 years that I have been doing this every bin that I have seen break has broken on the bottom.
Third is any reinforcing such as 2x4's should go on the outside of the bin, so you should have your 2x4 | plywood | place where the coal goes. Sounds simple but I've seen many customers place the plywood on the outside it. This works fine for a while but eventually wherever the screws or nails are in the plywood rots or weakens and it eventually breaks.
If built properly a plywood bin could last 20 years or longer, easily. Build it with treated lumber and it will probably outlast the stove. If you intend on burning coal for a long time don't skimp, you'll be glad you didn't in the future.