We recently installed a motorhomewifi.com 4G motorhome or caravan internet system, and this video shows how the kit was fitted. It's a fairly simple DIY installation, fitting an antenna to the roof of the van, and then routing aerial cables to a MiFi sat inside the motorhome which shares out the 4G (or 3G or 2G) network as a private WiFi network in the van. It basically makes it easier to get a strong, high bandwidth signal while parked up almost anywhere.
