Claire,
firstly welcome. The 540 has no specific quirks. As regards hard to come across, well that depends if you are after a specific year/spec in any eriba. I am guessing you say a 540 as you require two long seperate beds. If this is the case then it's the one for you. If you simply require a long bed then you should also consider any of the 55 series Trolls. This will open up your choice of vans available considerably as they have 2.0m beds at the rear and front dining areas that will squeeze 4 I believe.
Colin