i have a pair of brackets that were taken out of a Ford E250 van. See the pics you can see how the bracket at the rear conforms exactly to the curvature of the left side (driver side) of an E250.... note the 7 screw holes... the brackets are 16" square. they were originally used to house a 3 x 3, total 9 gang of 5" PVC pipe. the last 2 pics show the brackets installed as a PVC long-object carrier (like pipe, of different sizes, etc)
may fit other vans, but for sure an E250............