Installing an Extend-A-Stay Propane

Update to my situation. I went to a commercial propane dealer where I lived who said they can install extend-a-stay adapters and they were baffled by my setup. Talked to the mechanic and he said there was no way he could install it for me. They even even said if I wanted a permanent external tank like many of my neighbors they couldn't do it. They won't even fill my onboard tank if they are already at the RV park filling someone else's external tank. They said it was something to do with the pressure on their 100 gallon tanks is different than my 20 gallon, which I think could be BS because I've been at many parks who have propane trucks come weekly to fill onboard tanks. I called a mobile tech and he is going to come take a look for me. Hopefully he can figure it out. I really don't feel like packing up every three weeks to fill up my propane.