I don't have a garage either, so I keep mine in the house. No wife to bitch at me, so I can get away with it.
The plastics are easy. I use Pledge furniture polish on them. Keeps a nice shine and beads the water. Plus it has that lemony fresh scent which hides the fuel smell when the ladies stop by to visit.
On the painted parts I wouldn't worry too much about them since you have it covered. They won't rust and a lot of the parts are made of aluminum anyhow. Steel parts like nuts and bolts and the chain and rotors will need some care to keep them from rusting out in the elements. Even if the bike is covered the humidity will get to them eventually. I have taken a few of the small brackets off the bike and painted them to keep them looking good and prevent the rust. Stuff like the rear master cylinder bracket, reflector brackets and the brackets that hold the guides for the front brake hose. Keep your chain lubed (as you should be anyway) and it will not rust. Some of the nuts and bolts are chrome plated so they should last a while outside. The rest of the stuff you can spray with a good quality silicone spray and wipe off the overspray. Yamaha makes a good heavy silicone spray that I use on saltwater marine engines. Works good for preventing corrosion and rust. A lot of cheap Wally World brand silicones are too watered down to hold up for long. The Yamaha silicone goes on heavier and lasts longer.
Yamaha silicone spray
WD-40, CRC and the like are good for some things but don't use it on rubber or plastic parts. Eventually it will eat into the rubber and expand and soften it into a messy goo. WD-40 is a petroleum product, not good for rubber and plastic (including the wiring). Silicone won't hurt the rubber parts. Another good thing to do is to get some dielectric grease and coat the battery terminals and inside of all the electrical connectors.
The main thing is to not put the bike away while it's still wet. If you cover it when it's wet you are increasing the chances of rust to develop. I know this is not always feasable but try to dry the bike real good before covering it. Compressed air is good to blow water out of the little nooks and crannies that you can't reach with a towel. I have a compressor at home but a small portable air tank would be enough to let you blow out the hard to reach areas, then hit the rest with the towel. Rust and corrosion are hard to stop, so all you can do is slow it down the best you can by keeping the bike as dry as possible.
Of course there is an alternative to my method. You could take the SheWolf route and keep your bike encased in mud to protect it from the elements.
J/K Wolfie!