Chris, I hadn't the slightest difficulty parking in the streets around, on the Sunday afternoon last year. Try the roads off west, at right angles from Alcester Road (A435) which is where the entrance is, or was last year.
Music happens in a natural grass amphitheatre, out of doors, looking at 2 covered stages. (Performance on the 2 alternated, to allow for set up times.) If you've ever been to Sidmouth, think the Knowle arena on a smaller, more wooded and tussocky scale.... I should take your own rugs, or chairs.
There were plenty of food stalls and other stalls to look round.
Hope this helps,
Jane Cardboard Cutout