Ian, T-cut would be alright to clean the windows providing that you are careful not to overspill the paintwork, and that the T-cut is not left on the windows too long. T-cut contains a petroleum based distillate which attacks the outer surface of paint and this would be harmful to caravan paintwork since the paintwork is fine and thin (to reduce weight). On car paints there is little problem since there are many layers.
Working on the caravan windows, the petro-chemicals in T-cut, for want of a better description, melt the outer surface of the plastic, so when you buff off with a soft cloth, the scratches fade to disappear, depending on their severity. Another thing to try is brasso, the metal cleaner. It too has petrol based distillates. Either way, you should ensure that the cleanign fluid is not left in contact with the plastic for excessive time or further damage may occur to the windows, similar to a perishing effect. Clean windows and dry off with chamois, polish on with soft cloth and rub windows gently, allow to dry to haze then buff off with clean soft cloth. You will be surprised at the result. The use of an electrical buffer (that can be purchased at Halfords or Argos for between