Take a picture of the base and note which screws come out from where, ditto for any you undo internally as it can be a pain in the arse trying to remember where that tiny screw you have left was meant to go.
Have a search for "service manuals" too, a cursury search for that with the brand and model only led to a place selling replacement keyboards but a bit of hunting might turn it up. Worth contactin Evesham direct and asking if they have a service manual (chance are they'll say no and offer to service it for you though).