We put our ground feed into a standing bulk bin and it works well, although we feed it out in a week or two. If it's going to be full a long time you risk getting it damp from any leaks or even drawing moisture from the metal sides. I have neighbors with wood bulk bins they have filled by farmers exchange and they work very well also. We also have a Grainery with a concrete floor and sometimes we will unload the grinder mixer right onto the floor and fill buckets with scoop shovels as we need it, we don't leave it there long ofcoarse being concrete. not sure on the hammermill I was a kid last time we used one, we went to a grinder mixer in the early 90's and been using one ever since.

We use a Farmhand grinder/mixer, so I don't know about the hammermill. We used to keep the ground ear corn in a wooden granary, which worked well until the poor granary (older than my dad) finally started to give out. We now put it into the old granary inside the barn. Our barn granary has a concrete floor with concrete sides, and we usually put two grinder/mixer loads in at once. We usually have it used up in a couple of weeks, although it will last much longer. We avoided using that concrete granary for years out of fear of spoiling the ground ear corn, but that has not been a problem for the last two years.