Try the Caravan club sites at Cheltenham Racecourse and at Baltic Wharf Bristol. Both have large areas of hard standing and you should be able to park away from the actual racecourse at Cheltenham. Usually quite breezy too which helps. Baltic Wharf is in the city, and you won't get much pollen but you will get some of the normal urban pollutants.
I'm a sufferer to and have got it more or less under control with trying everything both prescription and OTC - now use Beconase with the occaisional Piriton. If you are really bad, your GP may be able to arrange desensitising injections - Pollenex - but while these work supremely well this is slight risk of after-injection shock, so they now will only do them as day-patient.
Do persist as the snuffle-free life is well worth getting.
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