[hexspeed]

Lastly, I can’t see where California can do anything against out-of-state coaches, only in-state coaches by which they can control it via vehicle registration, but perhaps I’m wrong…

Among other things, CA Senate Bill 210 states:
“This bill would require the state board, upon the implementation of the Heavy-Duty Vehicle Inspection and Maintenance Program, to provide mechanisms for out-of-state owners of heavy-duty vehicles to establish and verify compliance prior to entering the state.”
So, the CA legislature believes it has the power to prohibit non-compliant out-of-state vehicles from operating in CA, and CARB is formulating the program with those legislative mandates in mind. And, yeah, motorhomes are explicitly included in the definition of what is a “Heavy Duty Vehicle”.

CARB is in the final stages of writing and reviewing regs to implement the program. Only in the last draft (Aug 3, 2021) did they add the following:
“This chapter does not apply to:
…
Motor homes, as defined in this chapter, registered outside of California and never used for commercial purposes,
…”

Bottom line, out-of-state motorhomes are safe for now, but are viewed as being fair game for regulation should CARB deem it necessary in order to protect the citizens of CA.

Jim