Found these accidentally online- not marketed as RV/trailer windows
anymore- these are being sold for "sheds". I thought no one was still making them; and judging from some of the used prices out there that seems like a common misperception.
Note: NOT safety glass. But then, neither are any of our original jalousies, as I found out recently having broken one that still had its OEM "Hehr" sticker on it. Available in painted white or brown...dunno if they'll sell them unpainted. And CHEAP, compared to prices for used ones online, if you're lucky enough to find anything that fits. Screens are included.
This one (first described below) is a near duplicate size-wise of the rear side dinette windows
in my '78 Trillium
Link to source
Overall Size From End of Flange to End of Flange is 37-1/2" x 24"
Rough In Size 35-7/8" x 22-5/8"
Window is 2" deep
Other Sizes: 18" x 23", 24" x 16", 24" x 27", 36" x 23" and 15" x 60"