When we use "curve to mesh" to convert a closed curve to solid tube, the tube always distort at corners. Especially for those closed-curves whose sides are not of the same length. So I spent about 3 weeks to develop this tool. With this tool, we can easily turn closed curve to solid tube and remain its diameter consistent. 

Example : 

Features : 

• This tool is suitable for making tables or chairs supported by metal square tubes. If you want to change tube's profile shape, it can do that, too. But custom profile shape's diameter can't be adjusted by parameter in UI, you only can adjust diameter by scaling the custom shapes.
• I set default bevel weight on curve's corners, If yout only want to make bevel on corners, just add a "Bevel" modifier below and set "Litmit Method" to "Weight".

• If you don't want to make a full circle of tubes and want to have gaps in specific parts, you can adjust 2 parameters in "Gap" Panel. These two parameters can control gap's number and its position.

Caution:

Remember not to drag a point too close to its neighbour points or you will break the mesh.