18650 - 3S holder with thermal and electric isolation

This is not the most flush design, it leaves some gap to provide isolation. 

I used 2 clips of 1cm out of ABS and it turned out super nice at the first try. You can simply scale up/down Z to your desired dimension. The hole is there to pass through opposite end in 3S arrangement. 

If you'd like to play with thickness, cover the batteries entirely you can fiddle with the provided FreeCAD doc.