I'm going to replace the service valve on my tank, and want to replace the
propane copper lines while I'm there  (currently they're bent to allow for
the larger new-style regulator).

A couple of questions:
Is the flexible copper tubing they sell at the hardware store the right
stuff?  The lines on my van are much stiffer than this.  Is that just
because of age?

Is there an alternative to the rigid copper tubing?  Some kind of
high-pressure rated flexible tubing?

What I would most like to do, is run just one connection from the tank up
into the van, and then split the connection at that point, to eliminate the
length required by the T-adapter.  This because, apart from my longer
regulator, I also have a solenoid shutoff valve between the regulator and
the t-adapter which is connected to a detector in the cabin and shuts off
the propane supply in case of a leak.  As a result, the stock t-adapter
protrudes from the skid plate as I currently have it.

Thanks very much for any help,
Wes