Those of you who keep your bike(s) in a closed garage can skip this one completely.
I am not that fortunate, and keep my bike under a carport, along with my cages (except for my '87 GMC SWB PU, which lives in the barn).
So I bought a cover for the bike, one of the light weight ones that I can fold and doesn't take much room in the saddle bag. Even so, when rain is accompanied by wind (which it usually is around here), the outside of the cover gets wet.
One morning when I took the cover off, I found considerable condensate on the bike.
So, now, I hang a small work light (15 watts) on the handle bar before securing the cover. Keeps the "under the tent" space just enough above the outside ambient temperature to prevent condensate from forming on the bike.
A garage would work better, of course, but hey -- you do what ya can with what ya got!
Your comment about the 25 watt bulb reminded me of a question I've been meaning to ask about keeping the bike warm. Have any of you used an electric blanket to keep your bike warm for quicker easier starts?
PS I do keep my bike in the dry!!