I love Garth's reply, and feel similarly. But after a few decent winters of baseline trainer sessions, I didn't bother setting it up this time and am trying 1-2 runs (on foot!) a week. I don't enjoy running, but it's tolerable.
To the OP... If you're concerned about sweat and rust on a steel frame, consider zip tying an old inner tube around the upper headset and also where the seatpost enters the seat tube, to hinder sweat entry. Then tie an old sock or bandana above each, so sweat wicks away (and you can rotate those thru your weekly clothes wash). I didn't do any of this the last 3-4 winters that I had my old steel randonneur bike on a trainer, but my garage was quite cold and sweat was modest. As I recently migrated parts from that old frame to a new Roadini, I didn't notice any rust for example at the seatpost/tube junction. The seatpost admittedly took a couple taps with a rubber mallet to loosen up, but that's after being in-place for 8-10 years of riding in mostly arid Colorado climate (and not subject to too many surprise Rocky Mountain rain storms).
They sell those hammock-like elastic fabric sweat blockers that stretch from the seatpost to the stem. Funny things. I tried one my first few trainer sessions some years ago. Kinda makes mounting and dismounting a nuisance, so I tucked it away in a drawer. I'm not particularly concerned with sweat landing on the top tube, since it's painted and clear coated, and because any hints of beausage there would be fine.