Transporting a small dog in the trunk space

I am interested in securely harnessing a 10-15lb dog (small dog breed) in the trunk of the GT to allow the dog both comfort while being safely harnessed to avoind getting tossed about on sharp turns or sudden stops. I currently have a body harness that allows the dog to be strapped into the center seat in the passenger cabin. But when I have 4 other passengers, this is not an option and the trunk with the availability of the trunk passthrough (lowering the center arm rest) to let Fido know we are around seems to be a possible approach I would like to explore.

Appreciate your thoughts/ideas!