I;m not sure where your located but an upholstery shop here in Dallas has been able to fix and create some vool stufff for me over the years. One thought would be to have a shop make new canvas for you, all while you get to customize it how you want it, cool screens and windows, different options.
The prices have honestly ran about half what I would have expected for the jobs they have done for me over the years.
Check your area, ask the local hot rod guys who does canvas, hit the local campgrounds and ask fellow hybrid/pop up owners.
My connection here is at Lone Star Upholstery here in Lewisville, TX. I have seen some huge canvas projects they have done for boat enclosures and they were awesome!
Flower Mound, TX
2001 Jayco 31' Qwest
2011 F-150 Ecoboost
Lots n lots of firearms!