I intended add a note on flex parts today, thanks for doing the work for me 
Just two links to complement my review above:
- the model file with included rubber band and building instructions layout informations
- the rubber band itself, to be placed in Custom Parts folder as explained by Cam.

Just two links to complement my review above:
- the model file with included rubber band and building instructions layout informations
- the rubber band itself, to be placed in Custom Parts folder as explained by Cam.