I hook my 5er to my 500 gal propane tank every summer. To do that I needed a high pressure regulator on the tank, and a low pressure regulator outside the camper. Just like a house.
I disconnect the hose that comes off of the on-board tanks and attach the copper tubing to the camper's system at that point. (A hose from the regulator to the camper would be better because copper tubing can only flex about 10 times before it breaks. I just take a lot of care not to flex it when I'm hooking it up.)
This is just a comment that you can hook up a camper to a permanent type propane supply if that's what your circumstances are.