I won't be there, going on the 6th and the 26th June.
No garages but plenty of open space to dump your stuff, if you're on an organised day it should be safe enough, who are you going with?
If they've got an instructor its well worth the cost of getting them to sit in with you.
Usual advice applies, start off slow and build up gradually through the day, keep an eye on your cars vitals, brakes, oil, water, tyres etc.
Video of a lap at Castle Combe below:
http://s265.photobucket.com/albums/ii211/Paul86S2/?action=view¤t=cclap.flvIts a good circuit with some technical corners, brilliant fun, and very addictive.
Have a good fun day.
Paul