I use a an old Go750 in a semi-waterproof cover ( £12 on ebay), with a lead back to the battery via a USB plug. Does the job. As backup I use NAVIGATOR on my smart prone. The app is free and you should download the maps onto a 16-32 gb memory stick. You can download all of Europe onto a chip so that you do need access to WIFI or 3G or 4G on route. It works a treat. Richard