The general consensus is that the best combo is camp beds with quality SIM's (which vary massively in price).
We have double air mattresses on top of the camp beds, with sheets, fleece and duvet. If however I could afford a thermarest SIM I would definitely be sleeping on that instead!
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.