Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3629856.

Had a go at creating a custom template as a sketch in fusion.

Has user parameters for width, height and length. stil need to work out the compressed and expanded lengths but, some day..

Link to Fusion 360 project (sketch only): https://a360.co/3slneUe (new link 2021/08/14) (Don't download .dxf files they're static, but had to add something, added .f3d file after fusions butchering of the free version, vendor lock-in ftw)

For a printable things look at https://www.thingiverse.com/thing:2007634 https://www.thingiverse.com/thing:3627478