For the purposes of configuring the width and height on my snooper sat nav, what does anyone recommend I set the dimensions to . Cheers
What truck are you driving 
As an agency driver, its class 1. mainly Scania’s
To set the dimensions you need the height and length and weights even axle weights of the unit and trailer, as you may have differing trailers and even units you will have to change them day to day.
But you could set an average and be careful where you go checking the road signs (as you should anyway) 
It’s just the width of the unit that I’m not sure what to set it to
Same here with mine, I have a tape measure to measure flt mast heights on my bed but keep forgetting to measure the with of the wagon 
roughyed:
It’s just the width of the unit that I’m not sure what to set it to
2.55m / 8’6", unless it’s a fridge or something special.
Don’t make the mistake of thinking you’re doing yourself any favours by setting any of the dimensions bigger than they need to be - you may get sent on hairy routes to avoid bridges you could have safely driven under.