If you are in an exposed position I wouldnt do anything without a proper base and the thing coachbolted down into the concrete. And built by a company that is local and understands the wind speeds prevailing. Something with a proper concrete base would need PP if for horses, we have an agric holding of 40 acres but needed PP for the stables as they are horse-specific. We also had to build to building regs and do proper drainage etc. However it is worth it because it means you are all above board and there isnt that slight niggle with doing it without PP.
If you are more sheltered and decide to use the 'its moveable and temporary' argument for not having to have PP, check your local authority rules, (on website if poss to avoid alerting them that you're going to put something up). Dont take what a stables company tells you as fact, some of them vastly generalise and overstate the exemptions. In some locations the mobile stables/shelter have to have no stable doors, no base of any kind and be moved every 28 days, never returning to the same location......in others, anything goes as long as it has skids.
Also how you get on with your neighbours (present and future) could play a part if they are close. It only takes one to kick up a fuss and the planners then have to get involved...
For genuinely agric buildings (ie not horses!) on holdings over 5 hectares (I think but check), agric notifications apply. Buildings over a certain sq m have to comply with building regs (ours is just under the threshold, at 60x40x12ft as I remember, but planning while you dont have to put in full app you do have to submit an agric prior notification form and they have 28 days to accept as agric (then you can go ahead) or require you to put in for full planning. Under 5 ha more restrictions apply - check with planning office.