With the highs not even reaching the 70's and the nights getting cold now you'll do fine keeping minnows in a large plastic barrel. When I first started keeping 'em every time I came back from fishing I'd dump what minnows I had left in a 30 gal. barrel and they'd be fine without any kind of aeration until they got used up. It wasnt long before I bought a small couple small bubblers from Walmart and began buying by the lb. I got two 55 gal barrels from a car wash place (they give 'em away and get 'em quite frequently). You probably would be alright using one barrel, but I'd buy two lbs at a time and split 'em between the two barrels. I would recommend you buy the amount of minnows you think you'd use up in a month (even though they'll last longer during the winter months).