If it’s the older style open front canopy they don't make one. You can easily make your own to fit. I used Blue Diamond Treadlite breathable groundsheet which allows the water to soak away easily if gets wet – assuming the ground is not waterlogged.
The new front enclosed awnings are provided with a groundsheet which is the detachable bathtub style.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.