Hi, Craig! Since no Casita
owners have jumped in with a simple "oh, yeah, I have that, too, and here's what caused it and here's the fix," it looks like it may be something unique to your situation.
That means we're going to need a little more information to help you. How long does it take to develop (in days, not eggs)? Do you only get the rust when the fridge
is in use? What if you run the fridge
with nothing in it? Do you store anything in tin cans? You have been full-timing for five months?
A picture showing exactly where the rust streaks appear would be really helpful. The thread "Forums 101" near the top of the News and Announcements section has directions for posting pictures (see post #7).
There are a lot of smart and experienced folks here, but they need more to go on. There are more Casita
owners on the Casita forum. Have you tried there also?
My first thought- could it be the wire shelves? Perhaps the plastic coating is damaged or defective.
Best wishes figuring this out!