Are you sure it is actually leaking? I had the same problem, a few years ago and it turned out that the roof wasn't leaking, it was condensation. I just made sure the awning was well ventilated and never had that problem since.
We found that, when we were using the old style plastic non mesh type ground sheet, we didn't have a problem with condensation on the inside. When we changed over to the breathable, mesh type, we had minor codensation problems on the inside especially the roof.
Hi al thanks for the replies it seems that you all could be right,i have a breatherable ground sheet,awning skirt,due to the weather the awning was sealed pretty tight so pehaps it was condensation after all,as i have bought the fabseal i might aswell do the job it wont do any harml