Access to Bradley Fork tailhead is thru Smokemont Campground. This campgroud is normally open in the winter, but is closed until March 1 for water line construction. I was told at the Vistor's Center that it's okay to park on Hwy 441 and walk thru the campground to Bradley Fork. Just be aware that you'll have about a mile walk before you get to the creek.
Agree with Craig that Raven Fork probably isn't worth the effort this time of the year.
I've fished the lower reaches of Forney several times and found it to be very good. However its always been a couple months later than when you're planning to go. I wouldn't worry too much about your boats at the mouth of Forney. As for the car, the only place I've heard of trouble was cars left at the tunnel on the Road to Nowhere. That was several years ago and I think it was one group of bad guys and they were caught. I'm not familiar with the area you're looking at.