How do I install horizontal propane tanks in my Lance 1161?

I have a class b with a horizontal propane tank. When I purchased used there was a fill adapter to help access the tank. Some propane stations can not fill without using this adapter, and yet no one has ever seen one of these. Everyone that filled my propane tank when using stated that they have never seen one. Any chance of going to a dealer and having an adapter made so that you would just have to hook up the adapter and they could fill without removing from the tray.