I own a 2019 GMC SLT Sierra with a multi-pro tailgate. The opening between the main tailgate and the interior tailgate allows water, dirt and snow to come through the 3/4 inch crack between the main and interior tailgate. The very top lip of the tailgate between the two tailgates has a huge opening which continues to the bottom of the interior tailgate. GM failed install weather stripping or a seal in this area, so water, dirt and snow will seep through easily through the large crack. I have a Lomar Tonneau cover and when I went through a car wash yesterday, my interior box bed was wet about 2 ft in from the exterior bed. If you place a flashlight inside your truck bed and have a Tonneau cover you will see why this crack between the two tailgates allows so much water into the truck bed. If you view the photos attached, I have circled in red the area that a weather stripping seal is needed. My GM dealership told me, if I wanted a dryer truck bed, I should have ordered a Yukon. All owners of a 2019 or 2020 GM with a multi-pro tailgate need to express our disappointment with this design and demand that GM fix the design flaw.
Chev owners don't know how lucky they are not to have a multi-pro tailgate. I understand chev will be adding the multi-pro tailgate in 2021.-do=add#.url-do=add#.url