I've been thinking about adding felt to my channels, but I haven't gotten around to it yet. Because my glass slides in vertically, there's less friction, so it's less of an issue for me.
Also, 1/2" glass is way thicker than you need and that 52 lbs is going to wear on you. Consider switching to 3/16" or even 1/8" and find another use for those 1/2" panels.