Hi folks, sorry re being a bit tardy in Answer but presently not enjoying the best of health.
Sorry but have not been down to any part of Cornwall like seems like forever. Cornwall is not really "Motorhome" friendly by that I mean if you are under 6.5mts not too bad but anything much above that you are best sticking to the "A" roads, the problem with this is that the best bits of Cornwall are not on "A" roads but down single lane roads often with or without passing places. Camp site prices are mostly at least expensive even the smaller CLs and CSs and you really do need another form of transport to get around Cornwall.
You do not say how long you are intending to stay if you are only looking for a couple of weeks then I suggest that you think about what
StrandcampingDoonbeg has suggested and compare the cost of stopping in alternative accommodation either driving down (Car) (But not on a Friday or Saturday) or Fly and Hire this would give you the freedom to roam anywhere and see a lot more of what is a beautiful county.
As I said at the start it is many years since re traveled down and even then it was with a Caravan so that we had a car.