Probably not the worst idea. If it wasn't for this damned lock down, I'd sneak out and buy some primer. The can I'm using at the moment has primer in with the paint apparently.. One of those 2 kids driving me nuts at Bunnings 30 minutes before lockdown came into effect and me not being able to find what I actually wanted kind of purchases lol.
I've just sanded and sprayed another piece. 2 coats seems to be enough to fill in pretty well from I can see in the garage light. I might get the other piece finished off later and see how it's actually looking in daylight.