I think a photo is attached ? Nope - I guess not. Sorry.

My wife was throwing out an indoor clothes hanger for laundry to dry on so I tore most of it apart and kept the main upright support portion.  It turns out that the upside down 'V' design works well in the back of a pickup truck to support a tarp.

With the 4 legs fully spread within the box parameters, the top of the 'V' sits just high enough to rest a long piece of angle iron. I set the 'V' near the back of the box and cut 2 lengths of electrical conduit the same length as the legs on the 'V'.

I took an old fan belt and filed it down to fit in one end of the two legs to act as a flexible hinge. Once the legs are separated to reach the box sides, I strapped the top of the 'V' to the wood railing at the front of the box. The angle iron rests on both, front to back.

I put socks over the ends of the angle iron to eliminate sharp edges and lay the tarp overall. Then I weighted the tarp with empty plastic bottles half full of water. All set for winter. Hope that helps somebody (& I hope the attached image shows up)