Phillip,
The advise above is excellent, however it appears you have things together very well. If you have high clearance and 4 wheel drive the best place would be The Hunters' Camp Trail.
Directions;
Go to the first Bowen's Ranch via LA. North on 15 freeway through Cajon Pass. Exit Bear Valley Rd. Turn right(east) & go appx 10 miles to Central Rd. (BV Rd. starts with 6 lanes then 4, there is a movie theater on the right) Turn right at the light on Central & Bear Valley. 2 miles south to railroad tracks then a steep hill. After the hill turn left on the first paved road, which is Occotillo rd. Go 2 miles east until end of pavement. Continue appx. 1/2 mile to Bowen Ranch Rd and turn right (south). Take Bowen Ranch rd, which is dirt, bumpy and winding to Bowen Ranch entrance. You will see signage saying Bowen Ranch and a gate on the right. This is the road to the Freedom Trailhead. Go 1.7 miles to another gate turn left then appx 2 miles then another left turn. Go appx 200 yards and turn left again. Go 1/2 mile to large parking area. This is the Freedom Trailhead. CONTINUE ONLY IF YOU HAVE HIGH CLEARANCE WITH 4 WHEEL DRIVE FROM HERE. When you get to the bottom of the first hill you will understand why. At the top of the first hil there is a fence on the right. Look for a gate. The BLM request that we keep this gate closed. To open the gate pick up the post on the left hand side. Go through then appx 200 yards to Hunters' Camp parking area. The road ends here at the trail head.
Hiking down the hill to the main trail about 200 yards turn right continue down hill to the hot springs. The distance from this parking is 1.3 miles with less than 600 feet of elevation change. This is the closest parking to the springs with the least elevation change.
Please post a trip report and let us know how things went.
Happy Holidays!