Depending upon your location, finding a service center that recognizes the differences between aluminum and steel tanks may be difficult. When I phoned my nearby suppliers, they all were reluctant to address the 25-year old Worthington Aluminum tanks on my Argosy Minuet - - new OPD valves and recertification.
I finally decided to call my regular Airstream dealer and asked if their service department could handle the process as a part of my regular winterization. They had contacts with a propane supplier in their community who is familiar with the aluminum tanks and currently has my tanks in the process of refitting and certification.
Your best bet may be to call the service department of your nearest Airstream dealer and ask for a referral - - and I would suggest Airstream as so few brand X trailers even offer an option of aluminum tanks. If you plan to try to work with a local supplier I would suggest printing a copy of the Blue Beret/WBCCI article referenced earlier in this thread and discussing it with the service manager of the prospective refitter before committing to the process.
I don't know about the built-in guage sensors with the new OPD valves. Initially, it was indicated that they would not be available, but the last time I checked the Airstream Dreams web site and they were listing new Worthington Aluminum tanks with the level guage sensors. This would indicate that such OPD valves should be available - - another reason why an Airstream Dealer might be able to refer you to someone more adept in handling aluminum tanks.
Good luck with your refit!
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)