found an interesting article on this subject.
http://www.drivers.com/article/295/
It indicates that we (VX drivers) are guilty of some of the most common sources of the problems
1. lots of vibration.
2. poor visibility
3. being overweight (except etlsport)
You're already looking at softening the ride so you're on the right track. Attack one source at a time until you get the results you're looking for. Keep this thread going so that continued input can possibly help others who are suffering too.
I had a leg injury some years ago that caused me problems on long drives. The solution ended up being quite simple. I found that putting the bucket down as far as possible gave me more support on the back of my legs which kept my leg from cramping up. There won't be one solution that works for everyone but trying out different things opens up the realm of possibilities & everyone benefits. The first thing to try is more lumbar support. Try putting a small pillow behind the small of your back. Better yet, are there any car seat covers that have memory foam inserts? Check out these guys:
http://www.comfortchannel.com/prod.itml/icOid/428
Kind of pricey but you can return it within 30 days if it doesn't work. Or:
http://www.ultimatebackstore.com/pro...ination%20Pack