Sounds like a flat battery or blown main fuse.
Check your battery with a multimeter, you're looking for 12.7 volts or more. Anything less it may need charging or replacing.
Check along the red wire leading from the battery into the van. There should be an in-line fuse close to the battery box.
As Mr Grumpy says you should find a 20amp Battery fuse usually inside the caravan behind the Battery box. Often hidden under water pipes or heater ducting.