Take some 1" pvc pipe and stick the ends in the stake pockets on the bed sides to form an arch. This will hold the tarp up so the rain will run off of the tarp. I got 2 tee's and put them in the top of the arch and ran a 1" pipe between the front and rear arch. I think I am gonna put a tee in the middle of that pipe pointing down for a brace to the bed floor. In my case to the ground since I have no wood. I will be so happy to finish the shop. Not a perfect solution but it seems to keep most of the water out and lets the air move around under the tarp better. I made the arch as short as I could and still get the rain to run off. Cheap and I can sit under it and work on the frame. With a box fan blowing and the added shade knocking off the Mississippi August sun it is still darn hot. Under $15.
Neil
Neil