Those inflatable tanks at Dover might still look good from a satellite, but it would be tricky to assemble and transport them. They would need wheels and a wooden base, a small motor, and a driver. You couldn't just assemble them on-site or push them into position, being watched by a satellite in real time. Real tanks would have to arrive at the assembly area in advance, to drive around and leave so many tracks that it wouldn't be obvious that the fakes weren't leaving any. What about a heat signature? This is too complicated for me.