Even a normal transit won't fit them in flat as they are about 50mm too long. A LWB transit (or similar) or Luton are the only options to fit a stack of them in laying flat.
edit - I thought you could fit about 6-8 sheets in diagonally but just remembered that I had a SWB transit on that trip. No experience with Transporters and 8'x4' sheets but they're smaller than transits so might not even fit 1 sheet in.
Even a normal transit won't fit them in flat as they are about 50mm too long. A LWB transit (or similar) or Luton are the only options to fit a stack of them in laying flat.
edit - I thought you could fit about 6-8 sheets in diagonally but just remembered that I had a SWB transit on that trip. No experience with Transporters and 8'x4' sheets but they're smaller than transits so might not even fit 1 sheet in.