However, SWB, choosing a red London bus as your holiday accommodation of choice in an Area of Outstanding Natural Beauty is like waving a red flag at a bull. You obviously know that you don't have a good chance of getting planning and are prepared for a fight, but it seems a bit pointless. You're going to spend all that money buying and converting the bus but you'll only have 28 days a year to get your money back. So you aren't going to make a fortune and will have a constant fight with the planners, that they will most likely win in the end, once they realise your little game.
So why not get something more discreet and less obviously controversial, that you would have a better chance of getting planning for. Gypsy caravans, shepherds huts etc are possibly more acceptable to planners in an AONB. You are better using your time and energy fighting for planning permission for something feasible that can give you an income all year round, than trying to circumvent laws that at best will only allow you 28 days/years.