There was an advertiser for rubber seals in FMC magazine, but darned if I can find it now. Though your coach isn’t “vintage” you might check with these fellows,
https://www.vintagetrailergaskets.com/6-vintage-trailer-gasketsAlso see if this is a resource:
https://www.rvpartscenter.com/shop-by-categories/list1/rv-window-parts/screen-partsI’m not sure your windows are Hehr, but see if you can find something stamped on the screens or window frame so you can provide suppliers with a searchable part. These guys have been helpful to many here since Monaco/Beaver went out of business in Oregon:
https://www.nwrvsupply.com/As an aside, I have a fond memory of hundreds of whitefish (Squawfish) rising to a heavy hatch under the Hwy 287 bridge over the Jefferson River, where I mingled with whiteface cattle riverside. It’s a wonder the fish chose my purple haze parachute out of the millions afloat around it, but I had a ball catching and releasing a dozen or so, and they weren’t small… some a challenge for my 5 weight. 🐟
A visit to the confluence park, then a nice pizza in Three Forks before returning to the coach that evening in Ennis. Good memories to have.
Joel