I have a static caravan & I have a double socket fitted on a wall. The dry lining box is broken, irreparable. Does anyone know where I can acquire a dry lining box, 25mm deep. 35mm boxes are too deep for the narrow cavity. Some light switch dry lining boxes are standard 35mm deep, but have a 10mm spacer behind the face flange, effectively reducing it to 25mm. Does anyone know where I can get a double spacer from?