Hi Elliot / all,
This is a bit frustrating !
In this link it describes a procedure that seems pretty straight forward but my software (Home Designer Pro 2023) doesn't have the "wall cap" menu option so I can't delete the wall cap and it doesn't have the customer counter hole tool so I can't put a hole in the countertop. I'm going to follow Elliot's lead with the skinny cabinets.
https://www.chiefarchitect.com/support/article/KB-01264/designing-a-custom-drop-in-tub-enclosure.html