Looking back in my RCM magazines I found 2 articles that show seat construction techniques. The Feb. 2004 issue has an article " Finishing Touches, Adding Details ". Here the author Ken Estes, makes seats, instrument panel and decals for a Kavan Alouette helicopter.
The other is from June 2003 titled " Weathered Scale Cockpit Seats " by Gary Lennon.
The first article used green foam bricks from craft stores, and the second article used blue Dow extruded polystyrene. Hope this helps. Jim