Ulf: Haven't paid attention to whether or not you have the rear parcel shelf installed yet, but today I came across a very interesting Mopar Parts Information Bulletin, number 521, dated March 26, 1965 that discusses the "Shelf Trim Panel". All service replacements required "Paint as required" i.e. to match the replaced panel. It also says "Hardboard screen side up", part numnber 1304 AT6. It also lists a "One piece Vinyl Laminate" panel part number 1317 AT6.
I recall the '66 V200 have a smooth surface on the passenger compartment side, and don't recall what the underside finish was.