Just FYI---what you have are propane CYLINDERS. They are not permanently attached to the RV, and are designed to be moved around and shipped in the commercial transportation system.
A propane TANK is fixed to the RV and is generally not portable or intended be frequently removed.
The distinction is important, because the inspection requirements are different.
Cylinders need periodic inspections and recertification by a qualified US DOT-trained inspector. (These are pretty common, not hard to find.)
DOT inspection requirements, and list of qualified inspectors.Tanks are manufactured to standards set by ASME (American Society of Mechanical Engineers) and are not required to be re-certified. Of course it's a good idea to give your tank and valves a thorough look to check for excessive rust or damaged fittings.