I picked up this video during a discussion about how to make your own box; materials, height, width, length, that type of thing. I think the guy in the video has done a pretty good job. Apparently it took a bit of work to get the snow together and shape out the run-in, but once done, the snow lasted for the whole winter.
The box in question is 2′ wide, 18″ tall (around 12″ from ground when there’s snow) and 15′ long. Definitely a good length; long enough to try some combos. I wish my garden could accommodate something like this – and we had the weather to back it up over the winter.