Unfortunately, I just have a carport and purchased cheap dust cover I bought for $10 on eBay. This is fine in summer/ fall but does not even keep condensation off bike when it rains. With winter coming I want better, thicker cover to help protect my ex ( his first winter) from elements. Any opinions? Thanks
Whatever your final choice, ensure it "breathes". Whether that means it allows moisture out through its water-resistant pores and/or allowing air through the bottom, ensure to let it happen. Otherwise, you would be almost better to leave it uncovered in the carport and wash it down in the spring.
The Nelson Rigg covers (and I'm sure most name brands) have vents in them that are sort of hooded, so that rain and stuff doesn't get into the vents. It really doesn't matter what kind of cover you have, it's not sealed, and you'll get condensation and moisture on the bike. Being under a carport will help you. One bike I bought a long time ago came with a Dowco cover that was made of very heavy material that looked quite substantial.
One thing I do to protect my windscreen from scratches from the cover shifting around on it is to wrap a microfiber towel around the screen before putting the cover on. Not sure if this would be applicable to you.
A non-"breathable" cover will trap moisture regardless of the open bottom. Vents will help. However, since you are under a car port, professional covers can be had that are not waterproof, but are dust-resistant and breathes extremely well. I have such a cover and it kinda looks like a light cotton tarp. The material is not abrasive.