NSN 8340-99-800-0043 FV462749 appears in the FV432 CES for the Penthouse Conversion Kit as "Shelter Canvas; terylene and canvas, 24ft approx W, 14ft approx LG, w/end panel". Unfortunately the drawing doesn't make it clear what it actually does - it's not the penthouse tent itself, which is 8340-99-809-6541. I think it may be the forward part of the shelter that attaches to the rear of the vehicle?
Andy