Apparently Staedtler (who make lumocolor) offer an eraser which can be used for erasing OHP pen from transparencies. Worth trying this as an alternative to cloth and water.
There might be a space which could be dimensioned for the eraser. For example, the space beneath the day headers could be reduced to leave enough space above to store pens and erasers.
Apparently Staedtler (who make lumocolor) offer an eraser which can be used for erasing OHP pen from transparencies. Worth trying this as an alternative to cloth and water.