Propane tank certification? 2003 Thor told must be nspected

The employee said they all had just taken a mandatory course on filling propane tanks and were instructed to check age of tank by tag on tank (which mine has and shows 2003 build). Mine like most of yours is built-in and permanently attached to camper. Is there a federal site or documentation I can print out to keep with me citing the correct rules for this? Also, would like to educate the Southern States location that I routinely fill my RV tank.