Bought a bike cover 14 years ago when we went to Alaska. Was more duct tape than cover by the time we got back. Tossed it and haven't used one since.
For several years we bought cheep Wally World bikes and donated them after a couple of years. When we switched to recumbents we learned to live with rusty chains and mounting screws. We removed the seats on the recumbents.
Now one trike rides inside the rear of the car, and the second rides on top. Bought the second one with internal geared hubs front and rear kto keep clean gears. Still have to oil the chain (Boeshield) and mounting screws.
I think a good cover could be made, but would require premium material and seam structure = pricey. I don't think anything will keep the Alaska dust off the bikes.