How do you secure lumber (etc) to the beef racks?

The gap between the rack and roof is too small to slip a ratchet strap under. Anyone have tips on how to secure a load of material to the racks?

Probably most ideal is some kind of D ring that attaches to the camper rail system so that I can just avoid trying to attach to the rail at all, given that some piece of wood might overhang the rails and cover up any attachment points.

I haven’t hauled lumber up there, but have you tried Niteize Gear wrap ties? They’re probably good for short distances. A d-ring would also work.