Well, seeing as how you list La Mesa as your location, I would say do your shakedown first at some place like Ocotillo Wells before you start moving on to remote race courses!
Then there's always the Baja courses, but PLEASE make sure you bring a friend or 12 just in case.
Barstow might be a good place to check out, but I don't know how that works out during non-race events. I think that Stoddard Wells is a testing ground for a few race teams, but not sure who or exactly where (if you remember, I think that the MacPherson team got into some serious trouble and tragedy when they hit another racer during testing out in that area).
Gotta remember as well that there are a lot of racers pre-run the courses in regular ol' 4x4's. Better than getting stuck out in the middle of nowhere without your full support.
MDR is setting up the 300 course on Sept 20th. Good place to check things out. Suggest not going alone- even new truck can break. And the word prerunner on the bed side does not mean it is set up for hard core stuff. Go slow at first, learn your truck. The art to pre-running is not going fast, it is being able to save the equipment to get to the race truck.