Well I did 4 rolls in the shower, steamed it up good, closed the door and let it dry for 2 hours. When I first opened the door, there was slight cupping, but after about 15 minutes, it was business as usual. So I did a test, I souped 4 different kinds of film in the same mix of R09 1+50, HP5, Neopan SS, TMX and Tri-X all in 35mm. These were older rolls, so dev time did not matter, only being in the same soup did.
They ALL did the same damn thing! Tri-X was the worst, Neopan the flattest, but the differences were minor. Humidity was around 25%. Needless to say, I was ticked, ready to give up on 35mm. But then I followed some advice from earlier, before cutting the film, spooled it inside out and secured it for a day, it worked! All the negs are flat, good to go.
So this is the way I will do it from now on. As for the other 25 rolls that cupped, they live under heavy books until printing...
Good that you found a "fix" for the problem. I noticed you live in the mountains, and were able to raise the RH to 25%, you need higher RH to keep film from cupping. I live in the east and normal RH here is around 70%+ . Winter the humidity drops below that and I get cupping when drying film, then it flattens out. Shooting expired film has more effect on your film than humidity and especially developer choice, it stays in the cassette rolled tightly for too long. I would also think that the age of the film, having been subjected to many years of humidity cycles, even when frozen, that prior to processing and hardening the emulsion, it will leave the gelatin layer shrunken ever so slightly, that curl is inevitable.
I did not raise the humidity to 25%, that is where it was naturally, today it is around 22-23%, we are at 8,000 feet and have been in a warm/dry spell since January. Even though the test film was old-ish, it was still well kept so I still think it represents my issues well.
In any case, there are two ways I am going to combat cupping since there is not a lot I can do with one bathroom in a 2 bedroom apt. One is to use my Seal 500TX mount press with no heat on the negs that are already sleeved that are curled. The other is to roll the film I soup from now on inside out. Luckily, I did not throw away some 30+ cores that Dwayne's Photo sent my Xpan Kodachrome rolls in, they and the paper will be perfect for this.
Setting up a simple darkroom for hobby printing is easy-peasy......creating a consistent professional environment for fine art work is another matter, the details often being more expensive and numerous...