I not only have lights front (top really) and rear, but I have a large aftermarket visor on my helmet so I haven't tried any helmet covers assuming they won't fit. I've been intrigued for a while and considering crafting my own, but with my commute being right around an hour and the rain in Seattle during my commute almost always seems to be a steady light rain which isn't a problem at our temperatures. If it was pouring down rain regularly I might feel differently.

For now, a thin balaclava under the helmet does well to keep my head warm enough and breathes to let out some of the heat which I build up climbing all the hills here.

YMMV