I've had Typhonodorum lindleyanum for many years and never had a problem with rust, or anything else other than leaves eventually getting old. Nothing much seems to affect them. Do you have photos you can post?

As a matter of fact I do. It didn't show up until the weather got cooler. I had fish tank heaters in the water when I stored them last winter but was going to see if I could get away without it this year as they have gotten larger and are now spread out over 4 water containers. I'm starting to wonder if the cold water will weaken them and make them more susceptible to disease, however.

I don't know their cold tolerance but suspect cold water won't do them any good. They're not really like Colocasia type of aroids that can be stored. They produce a lot of seed which germinates readily so if you can get one to that stage you'll always have some small plants to keep going with.