I know this is an old thread - did this ever go anywhere?
You're not kidding about this being old. . .
I think Andre made some caboose bodies from the acrylic sheet, but never got around to hoppers. Perhaps because 2 and 3 bay hoppers are now widely available in 1/20th (Bachmann, Accucraft,) 1/22nd (Bachmann) and 1/29th (Aristocraft, USATrains) from those manufacturers.