You do need to make sure your RV will accept one of those devices. Not all will.
This ^^^is true. I found I couldn't add the fitting because my MH propane fittings are inside a metal box that wasn't big enough to accept the longer length of fittings with the attachment.
Remove the metal box? I had to do that.
Another issue is leaving the hose connected. Don't. I had a leak develop in my hose while I was away. Luckily, the campsite neighbor heard it and shut off the gas.
The port on the side of my Stay-A-While adapter is so close to the propane tank's cover door that adding the hose to it for the external propane tank will not allow the cover door to close. My RV tech installed a 90 degree elbow and a ball value to solve the problem. He told me that he adds the ball value because if I disconnect the external tank to be refilled and switch back to the onboard tank without removing the external hose, the external hose will slowly empty the onboard tank.
2005 Cruise America 28R (Four Winds 28R) on a 2004 Ford E450 SD 6.8L V10 4R100
2009 smart fortwo Passion with Roadmaster "Falcon 2" towbar & tail light kit - pictures