You know, it would have been really eas for you to have done a Google search for "Trailer Tent Cover" and checked a few of the descriptions, wouldn't it?
I found:
Heavy duty PVC cover
TenCate waterproof & breathable polycotton canvas
Big description here: http://www.kampa.co.uk/storage-covers/trailer-tent-covers
Triple layer SFS material beads water on contact affording maximum resistance to rainfall and snow
You get the idea
Anon, June 2016
