Propane plumbing questions

This year I plan to put a small Hot Dawg furnace in the detached garage. I will have to tee in to the primary regulator output and run a line over to a new secondary regulator. This is a 500# pig.
Back when I installed this system decades ago, I used 1/2" copper line. Is copper still the line of choice for running between the primary and secondary regulator underground?
I tried googling around for installation guidelines for propane and didn't find anything useful to me.
Thanks,
Wes
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Here's [art what my Google search found:
http://www.suburbanpropane.com/NPGA412-94.pdf
http://www.missiongas.com/underground-tanks.htm
http://www.gastite.com/page.php?pg=sc_propane_gas&idlink=link6
http://en.allexperts.com/q/Plumbing-Home-1735/Installing-underground-propane-pipe.htm

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