Roof Box

[GreenDog]

With a camping trip in Cornwall impending I'm thinking of getting a roof box for my Focus 5dr. Does anyone know the largest size that I'll be able to fit without stopping the hatch opening etc ?
Motor-World.com have a 320l one on sale for £70 at the min and although small it may be big enough to get sleeping bags, clothes and other items in just so the boot isn't quite so packed.

Thanks

[# Lord Lucan #]

looking for one for my galaxy actually now i come to think of it