By chance I was at W Yorks caravans today, and looking at the these vans. I picked up a brochure too, and the figures quoted by Lutz are accurate. I agree that they are very well made and have a durable solid feel about them. Being tall, the 6`5" interior height was welcome and unusual. The drawer bar seems and looks unnecessartily long, though it has a platform presumably for washing the front-which itself has an uncluttered 1 piece window.
The side bunk/dinette on the 540 is wider than similar designs. My 10 year old daughter thought the fixed bunks on the 520 were 'cool'-and they were sturdily constructed. To me, the payload of 130 Kg across almost the whole range would be too low-now if there was a twin axle....