Rebuilding 30's era Crane bath faucet . The existing pipes that connect valves to faucet are 3/8" ID copper, they enter the fittings and are retained by 1/2" female threaded nuts. When disassembled there didn't appear to be any ferrule, flare or sealant, except that someone had attempted to seal one join with string packing. I need to replace these pipes, space is tight where they are located in sink underneath, bulky fittings may be a problem. Location is not visible so appearance not an issue. Is there a better pipe material to use that would provide a better solution than the copper?

Hey, I'll answer my own question. Use 2- 12" braided supply lines, 1/2" FPT to 1/2" compression. The 1/2" compression threads are different so add 1/2" FPT to 1/2" compression ( male ) coupling, it's all available at home depot, don't forget the teflon tape, Packrat.
Thanks Packrat you make it sound so easy, and I won't forget the tape, Ratpack