In lieu of the Undercover XA2002 part, if you have a 2018-2019 Model 3 before they introduced the rear diffuser with the two hitch door, you can try to order the new diffuser assembly from Tesla that has the OEM door cutout/cover already. It’s part number 1135412-00-A
Give Tesla a shout to get the cost. Hope that helps.
View attachment 641033