A strange omission in most Cheltenhams is a light in the toilet compartment. This can be resolved by fitting a white plastic Britax awning light with integral switch, on the side of the compartment, so that the screws and wires run into the rear upper locker above the cooker.
Being designed for exterior use this unit is waterproof, if you are one of the fortunate few with a shower.

You can also try a battery cupboard light, there is a wide range readily available, search the web to see choice and prices.