If you think the 28 qt tub is too big for him right now, use some crumpled up paper to take up the excess space until he's big enough to use it. This method has worked for many of us.

I put hatchlings as small as 120 grams straight into 32 qt Iris tubs. With a couple of hides and some crunched up kraft paper in there to take up space, they feel right at home.