As example CWL has a railway station, they nenamed Rhoose village station 'Airport' and, I think, a bus shuttle to/from is provided, if Manston is trying to copycat SEN then Manston doesn't have SEN's advantage of a railway line passing by the end of the runway!
Having a railway station on an airport boundary is no guarantee of success. Teeside has Teeside Airport station and is the UK’s least used station in terms of passenger numbers with just 46 passengers using it in 2008/09