Answer:
The one-action rule that makes California a non-recourse state only applies to real estate mortgage loans. While some motorhome owners reside in their vehicles and may even claim them as a residence for tax purposes, they are not real property and the loans against them are not mortgage loans.
The loan you would have for a motorhome is either going to be a traditional vehicle loan or a specialty vehicle loan, and is therefore subject to the laws governing those loan types. Generally speaking a lender may pursue the borrower for any deficiency.