I've never seen propane eat copper pipe, I guess they're gonna have to go back and swap out all those pigtails and risers on those tanks we put in.
3/8 seem a little small if your going from 1/2, 1/2" copper with flare fittings is what we used on our risers.
What ever you do spray every fitting ,even the ones you didn't touch, with leak check(soapy water works but is not the "recommended" liquid), propane is not to be fucked with
Best solution, have your propane suppliers service crew come do it