I installed mine (a curt as well) without drilling or removing the bumper. There is a large hole in the left frame rail in the same location as the right side. It's hidden by the 2 pipes that go to the fuel tank. I removed the 1 10mm head bolt that holds the pipes & was able to move the pipes enough to get the fishwire & plate & bolt thru for the left rear most hole. It's a little fussy, but I didn't want to drill...
I didn't know what to do, so I didn't do anything
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View my fuel log 2018 Mirage GT 1.2 automatic: 37.3 mpg (US) ... 15.9 km/L ... 6.3 L/100 km ... 44.8 mpg (Imp)