That is a standard 'treatment' for glass windows. I would be careful on plastic as they are extremely delicate. It seems that almost anything will give scratches, that you may not even see, until the sun shines on them. Lots of water and a small amount of mild washing up liquid may be the best, but I am no expert on these. All I know is that even caravan shampoo can cause scratches on the outside as quick as look. They can be removed with polish, but it is hard.