Look at the pix I submitted.
You will notice a pair of black straps extending over the airplane from the shelf. They are 2" wide polypropylene strapping material with 2" wide Velcro sewn to each end. One strap from the front, andf the mating strap from the rear. One for each side of the airplane.
Install a brass grommet in the strap, and screw it down.
It only takes about a foot of Velcro on each end of the strap.