If you have a Plus 4 with the 2 litre Duratec engine the larger storm cover is a the better option as it will keep water out of the engine compartment.
The 2 litre Duratec does not have a cover over the spark plugs, and are therefore unprotected from driving rain water.
Same with the 4/4 silver top Zetecs - my spark plugs were rusted when I bought it and they'd only been in a year
