I think it depends on a number of factors, particularly whether storage is to be fully outdoor, under some sort of sunshade roof, or indoors (in which case probably don't need a cover.
If the former, I would be a little concerned about a roof only cover as there can be some very strong and gusty winds which could disturb a roof only cover and cause it to chafe. Bungee cords expost to full and hot sunlight for any extended period could deterioriaate quite quickly.
A full cover would probably be better. Someone on our usual site left their Bailey van there this year and had a full cover made by one of the well-known makers but approved by Bailey. It was silver rather than dark green which would seem to be a good idea as it would be more reflective than absorbing as a darker colour.
If outdoors I would suggest some tyre covers as well.
