If you have a Coleman popup with the channels already on top installed by the factory forget drilling holes in the roof of your trailer
Get 8 round top stainless steel bolts nuts and lock washers and grind two sides so that the bolt head slides snugly down the channels.
Drill the holes out in the four mounting brackets to fit so the new screws will go through. Assemble the cross bar and bracket, cinch down the 8
nuts and you are done. Solid as a rock, looks sanitary, You will have a great installation with zero drilling of holes in your popup trailers roof.
As Coleman accessories are almost impossible to find and costing a kings ransom if you do this is a great installation. I have had many Coleman popup owners checking this out. Next, install a bike carrier next to my Thule Accent 1600.