Many divers/tourists are taking the sleeper from Bangkok to Chumphon and then onward to the three islands in the Gulf. I did it one time yrs ago. Lomprayah used to have a small office right by the exit of Chumphon Railway Station but it is not the case anymore. It has moved about 300m down the right hand side of the station. I am pretty sure there will be rep aiding any would be customers coming on the sleeper.