We bought our silver tarp for about $35. Our camper opens sideways, so we use octopus straps to hold one end of the tarp to the side of the camper, the other hangs over the other end that is held up by the normal poles. I then have ropes going from the tarp to pegs in the ground. Half way along the tarp and depending on how long we are camped for, I will just have ropes to ground pegs or put poles up to give air space between the tarp and canvas, roped to ground pegs. The tarp overhangs all way round by about 25cm’s. Our tarp only covers the camper, not any awnings. Even just having the tarp lying on the canvas makes a big difference, but having some space is even better.
P.S. The ropes I use on the tarp have steel hooks, that I made, on one one end so I can just attach to the tarp without tying a knot. The other end is the normal spring type guy rope to attach to the peg.
Kevin