When you say seal the window I assume you mean the caravan frame , if so the water may be coming in higher up and running down between the outer skin(ABS) and the frame (Wooden frame with polystyrene insulation) and appearing at the bottom of the window. The window seal has a layer of mastic on it the outside lip and water can't get in through it. to check lift the inner lip on the inside , if the wooden frame is wet then thats a sign its coming from higher up , often it's a failure of the seal on the window hinge bar , particularly on elddis caravans (Xplore) but I have also seen it on Swifts and Baileys. The other fault is the top window seal , due to the angle and the section water sits between the bulb and the main seal and then seeps across the seal an drip down.