Henstridge is a very friendly field and a great source of cholesterol courtesey of the fine all day breakfasts available.
However, the parking areas in particular are in a dreadful state, and despite the assurances you have received, many have had their props badly damaged after visits there. I am not convinced that passes over them with the road sweeper are particularly helpful either. I suspect it dislodges as many new stones as it disposes of.
You can take all the obvious precautions and still be unlucky - be forewarned.
2D