When I mounted my Terrova I put it on the opposite side of the deck so I had 4 holes left where the old TM had been. I found plastic plugs at Lowes that fit the holes perfectly. They were even black like my deck so you never even notice they are there and they keep water from getting in too. The plugs were made specifically for this application. You may have some on your car of truck where it was predrilled for some accessory that was not installed on that model.
Just thought I would pass it on in case you need it.
Mark 1:17 ...I will make you fishers of men