When i built my model 5 outback there was no instructions to reinforce the trailing edge. So i used a can of expandable building foam insulation and filled the space in the trailing edge. Cut off the excess with a razor blade and coated the foam with epoxy glue. I heat shrank fabric to 350 degrees with [ NO ] bowing of trailing edge. It is very strong and lite. That was 11 yrs. ago it is still perfect.