No pics to share....
But I can suggest against the 55 gallon drum. You want something with more surface area on top. (more on that in a minute) Plastic would be my choice. Because metal would be more susceptible to temp variants than the plastic, I'd think.
Years ago a baitshop I frequented switched out the old metal tanks for large plastic trash-bins minus the lids. They then hung the aerators over the top and hooked up the water supply with PVC fittings.
Your biggest issue (possibly bigger than aeration) is a supply of fresh water as well as an exchange system for the old water... Just filling up a tank with the garden hose won't cut it unless you are willing to siphon off a portion of it and then top it back off every few days...
So why more surface area....? Nitrogen. Nitrogen is a byproduct of minnow metabolism. The only way to get rid of it is by disturbing the waters surface to break the tension so the gas can escape. Sure you're adding Oxygen too, but more importantly getting rid of the Nitrogen. By having a wider/larger opening for the tank, you are increasing the surface area to disturb with your aeration. That way you can get away with not having the water churn so much.