I just made one from a polytarp. Just rope beaded the edge to slide into the c channel that the awning goes into . Insert it from the back till it touches the awning and clamp side to awning and put a pole and holddown rope on opposite corner.seems to work ok. Did the same on my other camper also.
It was a rainy few days at Algonquin Prov park...tarps kept us dry.
Wayne --Belle River (Windsor), Ontario
2013 Sunset Trail Reserve 25RB..
2015 White Chev Silverado 2500HD 4x4 (6.0 l gasser)
2003 Mountain Star 890SBRX Truck Camper