Espar, a German company, runs North America out of Mississauga, near Toronto.
Here’s their site:
Espar - Dealer U.S. - Vehicle
Open Alabama on the dealers page and you’ll find service centers in Birmingham, Montgomery and Dothan.
This is the information Airstream should be giving you.
My all-diesel Airstream ARGOSY is powered by a Webasto coolant heating system and I have a Webasto diesel cook top as well.
Espar and Webasto, both German companies, make air and coolant heaters that are almost exactly the same.
Somewhere in my long main thread you can find lots of pictures and information on my Diesel Powered Trailer if you are interested:
All the best,