I have an Audi station wagon, which works extremely well for diving (doubles or otherwise) and is also a very comfortable passenger vehicle with good gas mileage. Unfortunately, they don't make the exact car I have any more, but they have a similar replacement.
I currently have an Audi Q5 and a Q7. Although smaller, the Q5 works out perfectly for two sets of doubles, an 80cf stage, a 40cf 02 bottle, large Rubbermaid tote, drysuit bag, undergarment bag, etc. Everything for a full day of diving fits, no problem. I'm a bit taller than Lynn at 6'2" so the floor height of the Q5 serves me better in terms of gearing up right in the back of the vehicle - set tanks up, don scuba unit, walk away. Perfect when diving at our local training quarry.
Previous A6-based Allroad had plenty of room (I'm guess that's what Lynn is referencing) but the back was too low for me to gear up right out of the car. Before I was diver I had an S6 Avant... and I'm waiting for them to bring the RS6 Avant back to the US. The floor might be too low, but who wouldn't want a 560bhp twin-turbo powered German station wagon...