if you are going "fast bags" your going to want to use larger diamiater lines with compressed air
if u are using the bags just to get in the weeds smaller line with a compressor and small resavore tank will do fine
as far as copper lines go i see them eventually rusting out some how and also not being very flexible in areas where you want the line to be flexible. you could use copper lines to your solenoid and then using the more flexible nylon line from your switches/toggles to your bags themselves ive never heard of copper lines being used myself it may be something new:bash:
Copper aka hardline is a pretty expensive option, it's been done a lot before but it's not really worth it for the most part. Extensive Metal Works down in Texas does it a lot. As for copper rusting... it doesn't rust it oxidizes but not like a iron would.
If you want to run some type of hardline it's easier to run steel braid but that is also just as expensive.
I'd say just stick to DOT approved synflex line. Much easier to run/bend and much easier to maintenence or change if something breaks.
I hope to start baggin it here in the next two or three weeks. I'm gonna run 2 7gal tanks in the bed with probably copper line coming from the bed into the cab, since I'm gonna run 1/2 manual ball valves in the cab. So, I figured I could at least run copper line from the bed to the cab and then out of the cab to the underside of the truck, and then run regular air line from there to the bags.