Hi first rule of planning is NEVER to show them all your cards! You must learn to listen to what they are complaining about and use their complaints to bolster your arguments.
When planners start waving around 'flood risk' as a way to deter you from gaining permissions you should have a good local architect to solve these issues for them, unfortunately planners dont like to give permission in fact its their job to stop developing on land, no matter how much you know they are talking crap, you can actually use everything they say against them, but the employement of an architect who is local enough to know them and ways round issues is absolutely vital when going for residential dwelling of any sort .
I dont know if your aware of this but you must use the 'health and safety' card, as a means to get them to allow you to place any building /caravan which has kitchens and bathrooms, because even if you didn't have horses and were just growing plants or mowing hay, you must be able to rest, wash, relive yourself and eat in a sanitary comfortable environment, and that also includes somewhere to sleep which all comes under health and safety .
Also permitted development rights include the siting of any towable caravan that is in good road legal order, but you dont need to actually have a caravan (these tend to *** everyone off) you can legally put up a shed and kit it out with a kitchen, bathroom and seating area,your job isn't to prove you are not living there, its their job to prove you are and that can't possibly be done unless you are under surveillance 24/7! And in which case you can file a complaint that they are ruining your natural enjoyment of your property and believe me or not it is taken seriously.
One way round all this is to have an address where they can send you letters even if its just a freinds house and you are telling them that you are commuting daily to tend to the horses and that in fact aids the means tested question they'll throw your way, because the situation means that you are tired and fatigued from travelling and because you are getting there early in the morning and leaving very late at night it has become problematic for you, (which again also helps them not to be able to prove you are living there because they physically cannot police that type of activity) ,you must use as many examples of why you need to be there for your animals safety and well-being, ill strongly advise reporting every single tiny incident to 101 and keeping a record of the reference to include in any planning application to support your means tested statements, because it will show how vulnerable animals are without supervision, include every single vet call out aswell. (all of which can be done without planning if you dont mind playing cat n mouse for a few years)
Back to the planning process if doing it by the book. Firstly you must apply for a temporary licence for a static caravan or similar, this will be granted if you meet the means tested criterias (which includes if you have earnt a min of 1 agricultural wage over the course of 1 year but you have up to 5 years to get to that point and its very low i think around 12k, it can be all of your family contributing to that but it must be earnt from the land and your operations from that land, ie making and selling hay, composting, raising chickens, wool from alpacas, breeding horses)
The council are lieing to you about your temporary stables, because all animals are required by law to have adequate shelter and that includes putting up shelters without the need for permission that is a fact btw.
The issues arise when buildings are over a certain permitted height, if they have concreted yards, if they have stable doors rather than gates or slip rails (one way round that is to tell them some are breeding stallions, and you need an exercise area for laminitic animals etc etc)
You can also extend every building every year within reason, after 5 years you are free from planning