How to use Ubuntu QML Dialog or other Popup without any buttons?

I am trying to make a modal popup where all there is is a progress bar, and when the progress bar is full it automatically closes, Dialog and the other popups don't seem to even show unless you set them up with buttons (not including Popover, that's too far off from what I want), is there a way I could get Dialog or DefaultSheet to work without any buttons?

Or else how can I make my own popup with PopupBase? That's what I'm prepared to do now, just not sure how, I know I would need to create a file MyPopup.qml, which then I could do:

MyPopup { stuff goes here }

But in MyPopup.qml would I do this?

PopupBase { MyPopup contents go here }

Wouldn't that be using it directly (API page says not to use it directly), and if so, how do you "inherit" PopupBase to create your own Popup?

If my question is confusing please let me know and I'll try to clarify.