Hi Magpie, we have exactly the same awning and know from having had one on our motorhome how important this central rafter is. Several people would come over and tell us that we should drop one leg so the water will not pool in the middle. But we always had it level with no issues because we had the central rafter and a nice taut canvas. Our answer for our Troll was to buy an extending stainless curtain pole (about £20 ) with some non-slip material wrapped around each end and for the belt and braces approach either bungee or strap in place. We have been away during huge downpours and it works a treat. Think we got it thru' Amazon. We also retro fitted Thule Tension Arms (about £30 ) which also stiffen everything up brilliantly, a must!