It probably is a little small to get it good and hot. Although you never know, depending on circumstances, it might work if it can absorb enough heat in the summer.
Something I ran into using a 55 gallon barrel was not enough air flow. I had painted it black to absorb the heat, but it didn't get enough air - should have drilled more holes into it. It is actually still outside, I have just been too lazy to drag the drill out to the barn and start adding holes to the thing.