This is pretty much what I was wondering about. For better or worse, Texas doesn't require the partition (section 49.031 of the penal code.) However, I didn't see the exception in California's vehicle code above.
Since a motorhome isn't a limo, section 23229 doesn't apply. If the partition is the legal requirement, housecar or no, I guess I'm going to get a hitch mounted cargo rack, which will comply with CA's laws.
I was wrong about something in my initial post about Texas. I remember livery vehicles used to be an exception, but it appears that no open alcoholic beverages are allowed in hearses these days.