No strap on main awning. How do I know the length I need?

Thank you, tenbear. It's a frightening thing that I'm doing and I wonder (often) what the heck possessed me to finally take this leap. Can I do this all by myself, at the age of 53? What was I thinking! It's one thing to fantasize and dream, but it's another thing to push all your money to the center of the table and lay your cards down.

I'm all-in and I'm not sure I have the cards.