Step 1: Buy hardware
2 x 1/2" thick, x 6" eye bolt w/nut zinc plated
2 x 1/2" nuts zinc plated
2 x Carabiners (locking ones are probably overkill, but get good quality ones that latch into a hook system when closed)
4 x 1/2" lock washers zinc plated
4 x 1/2" cut washers zinc plated
(image shows disassembled parts on left and assembled version on right. The washers will go on either side of the sheetmetal of the car.