Sorry to say this , but here is a quote from the DMV site

. I dont know if motor homes have somekind of special rules or not

.
Currently, smog inspections are required for all vehicles except diesel powered vehicles, electric, natural gas powered vehicles over 14,000 lbs, hybrids, motorcycles, trailers, or vehicles 1975 and older .
http://www.dmv.ca.gov/online/vrir/faqsmog.htmAnd one from the Bureau of Automotive Repair.
Beginning April 1, 2005, the 30-year rolling exemption has been repealed. Instead, vehicles 1975 model-year and older will be exempt. Therefore, 1976 model-year and newer vehicles will continue to be subject to biennial inspection indefinitely.
http://www.smogcheck.ca.gov/StdPage.asp?Body=/Smogcheck/doineed.htm