They used to add weight to the trunk in the show because they wanted a flat landing (much harder on the stunt people), but remember that this General is actually a rebodied Crown Vic, so it may jump differently.
I found a couple more videos on John's company Facebook page, but they've filmed in portrait mode, so I didn't bother watching them. In fact, I'm rather surprised that someone running a movie studio would film his "Extravaganza" on a cell phone held the wrong way around. Sorry, but portrait mode videos are a pet hate of mine.