Hi Dolittle,
I travel a lot across the border. I went to OCC on Monday and the border crossing has completely changed. As you are heading south, the parking lot on the right just before the border is the $7 lot. There are lots on the trolley sided, I do not know how secure they are. You have to walk across the border, towards the Trolley Station. One block past the Trolley Station, there is a walkway. You walk behind the businesses and to the "old" ramp/walkway. Up and back over to the side you started to catch your cab.
For the trip back, same as always but it was completely backed up with pedestrians, the line was easily 1- 1 1/2 hours. If I was having surgery, I would have preferred to pay for OCC shuttle. Maybe have OCC pick you up at airport. Why chance the rental car getting broken in to if your not using it??
Good luck.