There is not a custom fit option for the 2016 Colorado with flares. You can use the GB1223CutBT, they will be installed using the provided self tapping screws. With these flaps they do need to be fastened to a solid mounting surface because they are 5 lbs each.
Fastening them to just the flare is not recommended.
Justin
Verified Answer
Admin answered on 1/6/2019