I like this general idea, but I don’t think it can/should be accomplished with a list of width values. ColumnPanel is pretty flexible, and you can have arrangements like this in a single column panel:
The corresponding
col_widths is:col_widths: '{"BJRZJD":20,"LLJGPW":40,"XSYMNL":45,"AVGIDH":15,"VVYMWP":40,"VJWCVE":20}'
I don’t really have a constructive suggestion, unfortunately. It strikes me as a hard problem to both have the drag-and-drop “just work” as flexibly as ColumnPanel does and to also be able to fine-tune the numbers.