Hi TD,
I'm not aware of a map book specifically for caravanners, but clearly many of the issues of caravan towing regards suitable roads would be shared by HGV's. But when planning my own routes, there generally isnt a problem with motorways, or A class roads, so plan the bulk of your journey on those, and then when yo approach your destinatins most site owners offer caravan friendly routes to the site.
But as always regardless what the maps or sat nav tells you, you have to use your road craft and read the local road signs for narrow roads etc.