I'm guessing this is for one of them ladder racks where the ladder slides in against the ceiling?
Anywho... when I attached my strut to the top of the van I cut 3 pieces of 2" wide 1/8" thick strap (had scrap laying around). Cut it about 12-16" long. Screwed it up to the ribs with a handful of screws, then tack welded the strut to the straps that went across the ribs. Took it out, welded it up solid, painted, reinstalled... works awesome!
"If you call that hard work, a koalas life would look heroic."