In Reply to: No, but i just "egg crated" the back 1/2 posted by Jlam '75 on September 08, 1999 at 21:45:00:
If the bedding egg crate is not sufficient, you might try something more dense. I used that dense foam floor pading many machine shops put on the concrete floor to soften things up for their machinists. You could also use the foam pads for under your sleeping bag available at Academy or Oshman's for about $7. The more dense your sound insulation is, the more damping effect it has. However, there is a point where the density is too high and the insulation itself vibrates (maybe like hard plastic) and/or the sound waves are reflected.
Also, four pillows (sealed in trash bags) under the rear seat made a noticeable difference.
Since the ANC head-phones are cheap ($60) I'm betting the hardware is not that expensive. The price is probably in the "know-how" to set up the system and its association with avionics (just as performance=$$$ so does airplane or sailboat).
'72 BMW 2002tii
'94 LR Defender 90