We have an Outback with crosspieces that fold parallel to the car when not in use. We regularly stack two 12'6" race boards on top of each other and do 90-minute drives at 60 mph (97 kph). Been doing that for a few years with no problem. Just to be safe, we do lash a couple of straps around the top of the boards and through the inside of the car to hold the boards and racks firmly to the car in case of a big gust of wind. Probably should note that Subaru says not to do this and to use standard surfboard racks so proceed at your own risk.
