If i'm going to make tie-downs i'll need hardpoints, so i took a 1/16" drill to the roof racks.
I added fwd/aft holes in the top of triangles at the gutter, inboard/outboard holes in the same area, and an angled vertical hole in the center of the rack. All of these holes are pretty well hidden by keeping them toward center of wheelbase.
New straps were of course needed, so i knocked these together with some yellow nomex lacing tape about 0.080" (2mm) wide, some 0.032" (0.6mm) brass wire, and some CA glue. Making the hooks and buckles wasn't terribly fun.