Same thing probably holds true for your MH that holds for the Airstream trailers with keyless entry during those years. It's probably the same keyless unit made by Ford with the a code label on the module itself, as well as in some other inconspicuous location. Don't know of a remote specifically for the Airstream, but it seems to me that there would be remotes designed for the same mechanisms in Ford automobiles. I'd check car alarm dealers and such for that type of thing. As far as reprogramming with a new code, my suggestion would be to talk to Ford, since it originated with them.
If you search for "keyless entry" on this site you should find whatever info exists on the subject - not much but it may help nonetheless.