Trac Rack Metal J Hook and Neoprene Square with self adhesive:

Tenuous grip formed by the J hook as the J hook angles towards the top center of the roof, the Vanagons bumper move upward and outward from the van, so the two planes meet at the top of the gutters outermost point, while underneath, the J hook does not extend far enough under the rain gutter:

Twas perched on a juice bottle to get the right angle of the black metal bracket:

The black metal pipe fits just fine in the rain gutter, so it's not the issue: