Many years ago, my dad forgot to latch the emergency egress window in his fifth wheel trailer, needless to say it blew away while he was a long way from home. His solution, stop at the local hardware store. get some heavy duty plastic sheeting, some 90 MPH tape and secure the opening so it is rain tight. He then continued on with his vacation and took care of the situation when he returned home.
If you can go by a Forest River dealership during your travels, stop in and have them measure it for you. Take that information and give it to your dealer. This kind of issue happens all the time while people are traveling so there shouldn't be a problem having them do the measurements, even if it costs you a few bucks, just save the receipt and turn it into your insurance company along with the rest of the paperwork when you make your claim.
Moral of the story, do not open canopy in high winds.
Hope this helps, Sherman