"but the fact remains that a hollow tube is stronger than a solid bar of the same weight"
That is not necessarily true. Hollow tubes have a greater capacity for compression forces than a solid bar. In the case of tensile strength, a solid bar has more strength than a hollow tube. And the longer the member is, the less compression force it can handle. So in my opinion it would be a better idea to go with a solid member vs. a hollow one in terms of what would handle the variety of forces better (compression, tension, etc).