If you're storing bikes by resting them against each other, or next to items where you don't want chain oil and grime coming into contact, you could look at the Padded Drivetrain Protector by UK brand Fassa.
The protector slips over the outermost chainring and is then fastened by a strap that you loop round the rear wheel rim or frame.
At the chainring end there's a pocket that surrounds the front of the chainring, which prevents it slipping back when you tighten the strap, and also makes it relatively easy to 'lasso' the chainring if you're reaching from the back of your car to mount the protector.
The strap has a plastic thread-through tightener for the back end, although a velcro loop would probably be quicker and easier to use. There is, however, a removable velcro strap that sits atop the protector, which was handy on some frame designs.
The body of the protector is shaped to enclose the drivetrain — it's not a flat sheet of material. This adds extra protection, as does the padded nature of the protector. Some skinny profile pedals (cross-country and road) can be stored behind the protector, but I found it easier to have the pedal hanging outside it, with the cranks at a 5pm position.
If there was more room within the protector, it would be good to get the pedals in behind it as this would add further protection for the bike parked next to it — pedals are scratchy items.