Sorry for your misfortune!
With its tempered glass and no BS gasket that panel is sold as an assembly, OEM assembly includes using a hydraulic press to force the glass into the frame that is not achievable by the end-user. That is a flat window and is available complete for around $300 at VintageTrailerSupply
internet vendor, though they do come up for less on eBay and/or Craigslist.
If you have the itch to do a quick repair battle know it's going to take more effort to puzzle in a sheet of Lexan since either method should* involve interior liners off, remove weatherproofing caulk, cut rivets, remove piece, reglaze the frame and reinstall rivets & caulk.
Either way if you're not able to buck the solid rivets in order a few extra Olympic Shaveable Rivets as the clamping wings that spread do not always do as they're supposed to the first time, an obstruction or uneven inner surface and they can leave wonderful little gaps that siphons whole rainstorms into the interior.
If you really want to get it back on the road ASAP - lexan and double-sided VHB (very high bond) foam tape, round the edge of the acrylic sheet to get rid of sharp edges - and a very little caulk meandering the periphery to prevent water from reaching the foam tape...