There are two types of tanks as measured by their approval; DOT or ASME.
The common portable 20, 40, etc. pound cylinders are DOT type. They have expiration dates. Some are made specifically for horizontal mounting. An upright cylinder should never be used horizontally. It should never even be transported in the horizontal position. The DOT tanks made for horizontal use often have welded brackets like the ones referenced on amazon. This is to ensure the pressure relief and the vapor valve are situated above the liquid line. Home ground mount tanks are also DOT types. The horizontal DOT tanks are more costly than the usual vertical tanks we use on trailers and home grills (in equivalent volumes). Probably in part because of mass production of the 20's.
The ASME tanks are the type that are "built into" RV's... the type where you must take the RV to the propane dealer and they use a hose to connect to the tank in the RV. Those are
very expensive tanks. A new 5 gallon ASME will cost close to $400; 11 gallon maybe $600. I bought a used 60 gallon ASME from a wrecked class A a few years ago. I paid $500; new it would be in the thousands. ASME tanks do
not have an expiration date; no need to be re-certified.
