I realize that this discussion is a year old by now - but I wanted to add my 2 cents worth.
It appears, from all previous discussion, that the fifth wheel hitch is causing all of the fuss. If it is removed, and a flat deck temporarily installed to cover the rear of the frame, and photos taken with a motorcycle or ATV strapped to the deck (or driven there with full deck cargo, toys, & gear, ice chests, etc. for a weekend outing to the desert or the river) for their inspection - I would bet that the conversion to a motorhome would be no big issue - especially at a different DMV office - with different clerks.
One might even go so far as to install a receiver hitch receptacle to prove it is used recreationally, and hook a boat trailer behind it. It could all be re-converted to a fifth wheel configuration after the change to MH registration is approved. Perception is in the eye of the beholder. I would not mention towing a RV.
Another solution would be create a trust or business entity like a LLC or family limited partnership for the express purpose of owning title in a MH conversion - friendly state. The converted vehicle would be owned by, and titled in, the name of your "entity" that you control as its owner. Like a company - owned motorhome. You can own a company or trust in any state with no need to change drivers licenses. It would just be in California on "temporary business". I posted more on this subject on the escapees MDT forum at this link:
http://escapees.infopop.cc/eve/ubb.x...5406#401105406
Dan