I bought one of these for my car, it works well. My back no longer starts hurting after 2-3 hours of driving. Well worth $25, it won't fix your back but it certainly helps.
http://www.sportsimportsltd.com/inseluinairc.html

I've got a slight herniation in my L-5. It doesn't bother me every, except when in the car or thereafter.

I rolled a discloth and put it at the base of the back rest and behind the cushion about two years ago and now do 3 or 4 hour rides with no more stiffness than in my wife's C-70 convertable. Much cheaper. Ed

Just like most patients that leave out the most important information last :D ...A Lumbar herniation, no matter how slight is the cause of the back pain...position seating, ergonomics are exaccerbating factors.

I am assuming that this has been a chronic problem, and you've been seen by your MD, Physical Therapist. It would be a good idea to do your home exercise back program (stretching, stabilization) regularly.

I'm pretty sure that the herniation is a result of driving this car. Seriously. I've had back pain before, but it's never been this type of back pain. It's always been a muscular thing, or a pinched nerve type of thing (tingling down my leg).

I work out regularly (including my back - carefully) as well as stretching and flexibility. When I say regularly, I mean six days per week.

I folded up some cloth and stuck it behind the lumbar area of my seat. The lower back pad on the Recaro seat covers the whole lumbar area, so it wasn't a big deal to do that. It seems a bit better. Time will tell.