Technically they were just marker lights, but a lot of us CR modelers refer to them as class lights as well. They were supposed to be used on the trailing end of helpers or light engine movements, but in reality were turned on based on the whims of the train crews.
The MV lenses are long gone. I might have to give your epoxy-based recommendations a try to compare the overall effects relative to the effort and materials involved. Which one did you use on your UP 25502 caboose? The green lenses look really good.
M.V. Products #301 is the red equivalent of the green lens (#302) on that model. This M.V. lens is .052" in diameter or 8.3" in N-scale.
I also use M.V. Products #701 and #704 which are .046" in diameter or 7.4" in N-scale on some of my caboose marker lights, the 1" difference in scale diameter isn't very noticeable.
In the right light, they look illuminated, and at shows, I get asked quite often how I am lighting the marker lamps on my cabooses.
I'd do a search and see if I could finds some, especially the #301's which are in better supply than the others if that diameter is suitable for your application.
Here's a photo I've posted before of trains on my old "The Monument" Ntrak module with the M.V. lenses on the back of my mineral red UP caboose looking like they're actually lit...
Photo (1) - M.V. lenses on my brass marker lights on the back of my mineral red CA-4 UP caboose by Overland and white M.V. lenses class lights on my Kato F3:Cheerio!
Bob Gilmore