Craig, is there any chance of you staying at the coast instead? Much nicer camping and weather. Plus, you will be driving the opposite direction of rush hour that morning. Unfortunately, I do not have any suggestions for camping in the immediate Santee area. I'm sure there are some unimpressive RV parks though. The closest spot I can think of would be the Cuyamacas.
Paso Picacho is a developed campground and Stone Wall Peak is a really nice hike right across the street. If you are staying at the coast, then the best would probably be
San Elijo State Beach. I do not know of any good spots to "boondock" in the San Diego area.
Let me know if I can help in any other way. The folks at Aluminess are really nice and it was fun to see their factory.