ᐅ Expanding foam for temporary windowsill?

Hello, we want to install temporary wooden window sills, just for the time being. Which material is best for fixing them in place? Can I use expanding foam? Thanks

That will be difficult to remove later, of course. Maybe just apply 2-3 spots with foam or silicone. The question is, what does temporary mean?

Nothing at all. Just place it on top and that's fine. Or temporarily leave it out altogether.

If small children live there and might hold onto them, I would secure them.

Nothing lasts longer than a temporary fix...

I would align it and secure it with 2, 3, or 4 screws. That’s how we did it in our old apartment.