Have been leaving van hooked up when ever free camping for the last 8 years with the D3. I always set van slightly up at front so when it levels overnight it is level in morning, never feel it level but it does. It is only slight but never put your jockey wheel down as you may over load it when it levels. If leveling worries you like said before pull suspension fuse under bonnet.
3 Ton van 300kg on hitch.