While I was reading this Posting I realized I answered 2 years ago. I got some material from SMS Auto Fabrics. They have had mixed reviews but I found the exact match for my 52 Crestline. I picked it up my self during and RV trip. I just got an advertising email from them this week. Worth a try since upholstery material is getting scarce. They had a large warehous with tons of fabric rolls.
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I have also found door panel board, carpet, kick panels, package tray from Collectorsautosupplyinc on Ebay.