I created a parametric (OpenSCAD) tube mounting system based on the base-plate of the RELY1 modules created by obijuan (http://www.thingiverse.com/thing:13442).
We are using this to connect two of the modules together using carbon fiber tubing.
Note, this required changing two of the sources file from the original REPY1 module set slightly (to create the solid base). These changes will not disrupt the original REPY1 design.
Open in OpenSCAD to change the dimensions of the tube socket. Once printer, you can either use a hose clamp to clamp the socket tightly around the tube you are using or you can drill holes through the socket and tube you are using to fasten them together with bolts.
This is, as yet, untested. If we find that the bracket isn't strong enough, we might add supports to provide a stronger connection between the socket and the base-plate.