Typical awning lengths are 10' shorter than the rig stated length. A 25' rig is usually fitted with a 15' awning. Should you purchase an awning that is too long it can be shortened to fit you application.
Awning systems aren't inherently difficult to work on but they can be dangerous so please proceed with caution, and take the time to read through any manufacturer's installation and maintenance documentation before rolling up your sleeves.
We're here to any questions and offer advice if asked.
"One of the best lessons I've learned is that you don't worry about criticism from people you wouldn't seek advice from."
William C. Swinney