Good idea, Steve: this is not a new subject.
Now a couple of comments specifically about the options suggested in this thread (which happen to be quite opposite of each other):
I would not use solid metallic (copper) line all the way to the removable tank, even with the spiral in it. I don't have ready access to any of the federal or provincial/state gas codes, but I doubt this is allowed... a hose is called for.
On the other hand, hose for the whole run also seems like an undesirable plan. I would expect hose to degrade with time much more than metal pipe, so I wouldn't want a run of it hidden, especially under the trailer getting pummeled by road debris. It's also a pain to support properly.
I think the best way to go is to use the right material for each section (tank connection, under trailer, up to appliance), as described in those posts.
Same links with thread/page titles:
Hose/ connection to the rear from front of trailer
Propane: What kind of pipe is recommended?
Propane Plumbing
propane plumbing
propane hose
Fittings quick disconnect
Camping Equipment - Quick Disconnect Couplings,Camping Appliance Tees, Extend-A-stay