Tag axles were added by the RV manufacturers to the P30's to get higher GVWR weights as they were stretching the P30 chassis beyond its design limits. There appear to have been at least 2 or 3 companies that built these tag modifications, some perhaps better than others, there are certainly very different designs when it comes to the rear airbag setups used in this era, some are just helper airbags, other are mounted on large lever arms, more like real rear air suspension.
2002 Safari Trek 2830 on P32 Chassis with 8.1L w/ 400 watts solar 420Ah LiFePo4
2017 Jeep Cherokee Overland & 2007 Toyota Yaris TOADs with Even Brake,
Demco Commander tow bar and Blue Ox / Roadmaster base plates