My boat has been in a covered slip for 24 years, with a factory original cockpit cover over the cockpit. The original interior looks show room new. The Bimini top which is always up if factory original, I just clean it and 303 it every other year. Gel coat is still glossy.
Snow though rare can be a problem, I've seen boats here in North GA sink because of ice and snow. You can say, well I can clear that, but it gets really tough to get to the boat when the dock or gang planks are covered in a sheet of ice. I had to save my neighbors boat a few winters back by motoring up with my boat, boarding and clear the ice and snow. A real PIA and very dangerous work.
The way to deal with spider poop is to wipe down bow rails, Bimini top structure and dock lines with Ortho Home defense. It is good for 6 months. The only problem is you have to re-apply if you have rain blow on the applied areas.