If I lived where the temps got stupid low (like the northern tier upper mid-west) I would probably put the cover back on every mid October, and then remove it in late April (to retain a little more top end engine heat).
But since I do not live there, and it has not been getting very frigid here lately, I just leave it off, and 'live' with the resultant slightly louder injector tick, and valvetrain noises.