Good morning, Ben,
The Transit has a cargo holder fixture running the length of the van, so I pop riveted the bracket to the fixture and then through the interior steel of the Transit. The L-shaped bracket is 25 x 3mm galvanized steel strap from Bunnings. The pop rivets I used were 3/16??? type, with a depth suitable for that position. I used 2 x rivets for strength. The bracket then attaches to the aluminium leg of the board support frame by a bolt and locknut. A steel strap is used on the locknut side to spread the load of the washer and locknut from the aluminium board support. I used this arrangement at the front and the rear of the board support.
At the top of the support I used strap steel pop rivetted direct to the Transit steel. The strap is bent so that it attached directly to the horizontal support, but also matched the angle of the Transit steel. Brackets are placed front and rear, like the lower brackets.
There are 5 shelves in the board support frame and, when fully loaded, there is a large swing weight (going over light, bumpy ground). There has been no loosening of the any of the attachments to date (just over 12 months in service).
On the rivet gun side, I was using a standard- handle rivet gun (
www.bunnings.com.au/stanley-heavy-duty-contractor-rivet-gun_p5911947), but was finding it hard to use in confined spaces, particularly when using 3/16??? rivets. I changed to this,
www.bunnings.com.au/kincrome-280mm-short-handle-rivet-gun_p5910185 and it solved the problem.
Hope this helps.