Why not get one of those pop-up tents and put it underneath? Make sure it's the one with end opening as some are side opening? They can be got quite reasonably at the moment ans, as it will be under cover, will not need to be top quality water repellent, i.e 2000 hydostatic head or less.
------------- Mavericks don't get to lead the herd - not that they want to!
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.