Larry...
The US Federal Government has jumped in and regulates them.
Manufactured homes are somewhere under HUD
Their site associated connection are regulated by the NEC/ States.
Because road-borne anythings cross state lines the Feds have long regulated them.
As a practical matter, the methods and fittings seen in manufactured housing are often identical to that of RVs.
Unlike stick-built homes, it would be most unusual for specific construction inspection for either manufactured housing or RVs.
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In either event, I'd run away before I ever got involved trying to correct wiring problems in manufactured housing. They're built to be built -- not repaired.
