I'll put in an east coast plug for the Pine Barrens Adventure Camp. http://www.pinebarrensadventures.com/
I'm not affiliated but have taken 2 of their classes. I also think they were recently renamed.
They are the same guys who organize the Pine Barrens 300. They are extremely skilled and can cater to all levels of skill. Just be prepared for lots of sand. It really improved my big and small bike skills.