During in depth inspection of my orginal LP system, I found wear/rub marks on the copper line in several locations, plus most of the shut off valves were corroded/rusted in the open postion. I purchased everything I needed to completely replumb the copper portion of the system at Lowe's IIRC the total cost was under $200 and I have a 31' so there are some long runs. The rubber hose between the regulator and the main copper line came from an LP supply house, the pigtails came from a camper salvage yard for $5 each
(just happened to be in there and they were brand new still in the package in a salvage unit) My regulator has tested out okay, I may replace it anyway because the red flag is hard to see. Tanks have been recertified with OPD's installed. But I may upgrade to 40# tanks in the future....
The only places that needed any type of sealant were at the ends of the rubber hose between the regulator and the main line, and where the pigtails screw into the regulator, I used teflon tape in those places.