We use an old leather suitcase that I found on E-Bay - for period effect and style. We have a 90's 4-seater with a standard stainless steel rack on the back that holds the case like it is on a shelf. I have lowered the rack about 85mm by getting replacement rear stays made (Heart of England)so that with the hood up I can still see over it in the rear view mirror. We drive the motorway from Bilbao to Biarritz and beyond a few times each year, so I feel a lot safer if I can see the Spanish and Portuguese lorries following me.
The case itself does get wet, but it looks right. We pack everything inside it in a big strong plastic bag and we have had no problems at all. That leaves the interior space in the car for wine and other comestibles.
A different solution, probably peculiar to our type of 4-seater rack, but it works for us.
