Picked up some rear lapbelts at O'Relieys to put in my Trabbi. Mainly to hold my daughter's car seat in place if case we want to make it a family day in the Trabbi. There is a threaded hole for a shoulder belt covered up with a clear plastic cover but I am not seeing any pre-drilled threaded holes in the floor. Am I not looking hard enough? Or do I need to drill my own?