My son bought me the Syrius S2000N version of the Ventura Sat Nav system from Snooper a few years back now and it is a fantastic piece of kit.
It is designed specifically for caravan and motorhome use.
You simply enter the dimensions of your vehicle and Ventura will do the rest working out a route that is practical and safe, avoiding legal height, weight and width restrictions.
I have tested the device extensively abroad and in the UK and it has passed with flying colours.
OK they are a bit more expensive than a standard Sat Nav system, but it is a small price to pay, to avoid the horror stories that you here about, as vehicles become stranded in narrow lanes.
One of the great features that I have used over and over again is its campsite locator, which has access to thousands of ACSI sites and this has been great for locating an overnight stop and planning a trip as you go along.
You are able to easily convert it for car use, so you can switch between using it in your motorhome and car.
As you would expect, with all electronic devices, they are subject to continual improvement and you can see all the latest singing and dancing devices at their website and also the full range to cover all budgets.
The only thing that I am not happy about is its window mounting suction device, which has proved very temperamental and I am reluctant to pay for an expensive replacement and end up with a similar problem. It can be very frustrating trying to get a firm attachment.