IMHO if you're towing something big or driving something big you should never rely on any gps unit alone. There's enough computer based imagery of routes to do your research on the approaches TY sites.
There's the thing. Four instances that gave rise to this question are (mostly) good examples of how pre-research doesn't always work.
(1) Going to a campsite near Stourport on Severn. Research on google maps, no issues at all that can be seen, brain absorbs instruction of "go to <town> and turn left", send location to car satnav via "share to the app", visually all ok. It is only after the event I discover that the shitenav in the car has decided that the closest road to the geolocation shared was the byroad on the OTHER side of the river. That in itself wasn't the real problem, the real problem was, how to get out of it. I turned left instead of continuing, roads looking similar at the start, but they weren't equivalent. Ho hum.
(2) Going to a campsite in Norfolk, on roads I know well. Poodling along the road between Swaffham and Fakenham, we come across a Mr Policeman standing in the road with his hand up "thou shalt not pass. Verily some silly bugger hath smashed himself and others up. The queens road is closed." Not something you want to hear in Norfolk, tugging a caravan.
(3) Going to a campsite in Suffolk. Approach instructions read carefully and noted, including single track approach. What we weren't alerted to, by the instructions or by the Satnav, was how easy it was to miss the turning. Again the question arose how to get out of the predicament, which turned into a mile of single track mostly without passing places but with good sight lines.
(4) Going to a campsite in East Sussex, again prepared with directions, the junction off the A-Road is confusing and signpost in instructions is not present. Getting out of the resultant wrong turn was amusing.
Arguably the first might have had a better outcome with more incisive preparation, but the other three are instance where no amount of pre-preparation would have helped.
I've now bought a camping road atlas, which likely has as much info as the satnavs, and it looks to me that will be sufficient.