Summary

After many trial and error, finally I can finish this double wall project to create vase / cup/ pencil holder even planter cause its parametric (with some adjustment to printed it well)
Using what I called pre-sliced technic we can guide slicer (here I use Orca, other slicer maybe behave different) to slice the design exactly like we want.
For the Included STL Im using 0,6mm pre-sliced line height to be slice on 0.3mm (or 0.2mm if you want) smoothly without missing layer. all layer double walled as on setting with top layer (2layer if sliced on 0.3mm) using max rib to close the top
Using the vase generator we can slice many type of vase, cup or pencil case or small storage (using 4side) and spinning (or not) the layer smoothly.
Caution: default parameter is using non pre-sliced technic (0.12mm line height) to speedup OpenSCAD preview render. you need to change it from 0.2mm to activated pre-sliced feature and after waiting the preview render it will display different look. Need nightly build OpenSCAD to speedup render then can save as STL (or other as u like)

Update 20/9/2025: Added Quad wall for better watertight and wider wall thickness, sure double the filament used and more time to print. Now its use separate original qdwall.scad file (included here) to help arrange and easier update later
Update 14/9/2025: Following update on my double wall design: Add rib on corner. Also arrange customizer for custom design so can be show at nightly build OpenSCAD, Sample not updated, as usual old OpenSCAD code removed
Update 3/9/2025: Add top and bottom max rib to parameter (using pre-sliced layer). Bottom max rib help to enhance watertight, tough when I test it still leaking via layer change (maybe need more flow). Included sample updated too

Included vase Im using 72mm diameter 210height (need easily divided by 0.6/line height) 11 side polygon with classic style, 6rib each side 2.8mm wall thickness. Even with vase mode It still need 3hours to print (with regular no infill still over 5hours). Reduced speed maybe need longer but sure more smooth result :)
Need to activated Vase mode / Spiral vase in Slicer, 0.3mm layer height, line width
can be set 0.48mm or more to add strength. I'm accidentally forgot to set this and still using 0.4mm but seems not quite right / still have some under extruded (maybe because speed to max also)
With proper setting , I guess it is watertight as no gap in the design/print.. maybe need further experiment :)

Enjoy