RE: Propane Tanks
Okay, found this in the archives, part of a message some years back:
(note that the link at the top is dead)

According to this site:
http://www.recvehicle.com/propane.html
"vertical non-stationary" must be updated.
And the second paragraph says a lot.
" The 1998 Liquefied Petroleum Gas Code section of National Fire Protection
Association (NFPA) Standard 58 called for the installation of OPDs on all 4
to
40 pound vertical DOT cylinders manufactured after September 1, 1998. The
2001
version of the same code states that horizontal cylinders are exempt from an
overfill protection device (OPD) retrofit as long as the cylinder was
manufactured prior to Oct. 1, 1998. That means that these cylinders can be
legally recertified after 12 years without making modifications. The tanks
mounted to motorhomes (designated as ASME tanks) are not subject to this
regulation. "