I do not use a cover on my MS, however, I've had great luck in the past with custom covers from Covercraft -- both for outside use, and indoor dust protection. I just checked, and they make covers for MS in varying types of material depending upon your needs. I can't tell from their description how they handle the charging port, so you may want to check with them before you go too far (I'd prefer a Velcro flap so I could charge while the cover is in place.)
FYI, Covercraft makes a number of OEM brand covers -- IDK if that's true for Tesla or not. Take a look at Covercraft's website, and then if you find something you like, shop around for the best price. You'll find a number of Internet Auto sites that will drop ship a custom cover from them -- generally with better pricing, free shipping, and/or they throw in a bag to hold the cover when it's not on.