Should you cover your bike at night?

I used to, while touring, cover my entire bike with something like a extra large hiking pack rain fly, especially if I'm in very rainy areas, or leaving the bike for prolong periods of time. Say, I'm going out for 3 day backpacking trip myself: I'd cover that bike up.

For usual tours, I don't do that much. Usually, I'll pick a spot for the night that has as much coverage of the sky, so that if it does rain, I'm not in it. Easy enough to find a nice tree to lean the bike on. Keeping a few sil-nylon stuff sacks handy isn't a bad call to cover your seat - always something you can reuse for other purposes. Even when I've gone on backpack-less trips, I sometimes bring a very very stuffable sil-nylon backpack with me, in case I want to get a whole ton of groceries for a stretch.

Some things that can rust, that can also be a bummer are chains. If you're worried, you can always give your chain a nice coating before bed, and then wipe it down in the morning (and perhaps give it a few drops before going - depending on the manufacturer's recommendations).

I've used products to stop rust from happening inside your bike's frame - a nice, messy winter project - the bike basically has to be stripped from most everything and hung in strange ways a coupla times. Can't say I ever had any problem with rust destroying a frame, but I don't know if my frame was ever put to the test.

Things that you don't want water in, take a bit of water pressure (like when you use a power washer), or a complete submerge before I get a little anxious about water.

I'm far, far more aggravated when wet roads/trails make a mixture of grittiness that that splashes on my drivetrain and gets into my brakes.