Maybe some more info on what the problems seem to be as it is a pretty normal thing and much of the time it just needs some different type or size of fittings or hoses. Much depends on what use you want to make of the addition.
From comments I see the main confusion seems to come from using two regulators in the same line. If you want to use a grill and it has a regulator already, it needs to get gas from a point before the regulator on the RV.
More info on what you have and what you want to do?
Whoops! should have waited four minutes more?
Lots of videos and none are pros but this is one that works.
https://www.youtube.com/watch?reload=9&v=Rucge4w1UGA
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Richard
Why no RV year, make and floorplan on MY signature as we suggest for others?
I currently DO NOT have one!