this question has definately caused a wide spread of answers, so here is the expaination.
Aluminum wiring: commonly found in MH from 1964-1975
Polybutelyne plumbing: commonly found in MH fom mid 1960-current
Drywall: not normally used in MH until the late 1990’s, paneling was the norm
Plywood flooring: was and is the most common floor material for MH
Does it depend on which state the MH was manufactured for?
El Cajon is manufactured home city here, and probably 25% of my inspections are MH. I have yet to see aluminum wiring or polybutylene wiring in any of them (I’m presuming that your “Polybutelyne” is simply a misspelled “Polybutylene.”) in my 4½ years. And PB is commonly found from 1960-current? Meaning 2006? Really? I thought they quit manufacturing it about a decade ago.