Here is a script used to thicken a network of lines which could have a normal direction at each node.

It is similar in function to Cytoskeleton. It is an extension of this tool discussion.

It output mainly quads and sometimes triangles if some lines are not connected. As half sections are quite whatever you want it could be possible to make watertigh model with some smooth exterior and with interiors fins in order to have a better rigidity and a low weight. The script provided contains many examples of use. 

As inputs 

Necessary

* Points (P)

* Connection between points (LP)

* Point to points connection (PP)

* and a minimum one width (WidtsAtPoint), or a width (radius) for each point. 

Optional

* NormalsAtPoint, you could provide one normal per point in order to orient sections

* Number of sections is the number of sections used to generate the mesh (minimum 2)

* Striction a numeric value between -3. and 3 used to modify striction of nodes

* The sections definitions is given through to same size list of double 

  * Lateral coordinates : first and last lateral coodinate must be 0.0 for watertight mesh

  * Height coordinates

Output :

* Many meshes which could be joined

P/LP/PP comes from topology of network, you could use SandBoxTopology plugin or mine component