I have decided to create custom html modules using Seblod instead of Joomla's custom html.
I wonder if anyone has an alternative method....
I create a content type based on Article Object.
Next I add an article so that there is one piece of content associated with this content type.
Each time I want a custom html module,I create a List & Search type that pulls this article based on it's id (using live value). In the item or list view I add the title (set to hidden - it needs a result of some kind in the view) add whatever fields you require, maybe the free text field etc. and then create a variation override in which you write your custom code.
You then create a Seblod Search Module and display this.