I know it wouldn't help those trying to fill open auto racks, but what about an etched metal silhouette insert for the RC enclosed racks? I don't think it even needs to be 3-D. It could just be a piece that you fold into a upside-down "T" shape that stands up in the center of each deck. They could be made with variations for pickups, SUVs, mixed loads etc. Make them generic to avoid any licensing problems.
Even though engineshop's efforts are innovative and commendable, I almost think it would be better if the silhouttes were painted black. As has been pointed out by others in the past, RC outdid themselves on the see-through effect on their racks. You shouldn't be able to see through them that easily. A simple 2-D silhouette painted black might work to subdue the effect. Anyway, it would be easy to do a trial with artwork cut from cardstock to see if it's feasible. I might try it if I have time.
Just thinking out loud,
Pete