The Access Code is quite clear, There is a RIGHT to wild camp for walkers, cyclists, horse riders, canoeists. ie lightweight camping, away from habitation, etc. "Access rights don't include motor vehicles". Camping in your motorhome may be tolerated, although land owners have the right to prohibit parking on their land.
So, yes, you may be able to camp informally in your motorhome (or caravan) as I and many others have done, but there is no statutory right to do so. It all relies on people being responsible, as all of us on here are. Unfortunately some are not, and I read there is an investigation into someone dumping their toilet waste into a public drain on the NC500, which, if true, brings us all into disrepute.