When you move into California, and have to register your motorhome and cars, they ask on the form what day you started working in California, and other 'difficult' to answer questions if you are trying to avoid the tax man.
Why complain? Well I guess anyone getting the shaft for $1000 or so would complain. However in California, where you can buy a $400,000 home and pay only around 1% tax each year, (well close - say $4,100 or $4,200 depending on the local tax on top of the basic tax). Here in Oregon, you can buy a house for around $250,000 and then pay close to $5400 in tax each year. A $400,000 home would have close to $7,900 in tax - at least near Portland OR.
So we don't pay sales tax, however the roads still need to be repaired, the trash picked up, sewage taken care of, fire departments funded, and all that. The money comes from someplace. Not sales tax, but much higher property tax per $1,000 in home value.
We also have a per foot length registration fee. So my 30' motorhome required a $310 fee for that the first time it is registered in Oregon.
Sure you can "Legally" buy a motorhome out of state, and leave it registered there for a number of years, then bring it into California. It will save you perhaps $1,000 - $1,500 in tax and registration fees. However you will be paying for storage, not getting to use the new to you RV for a while unless you take a long drive in your car to it's location. And several other dis-advantages.
You can also look at a small corporation in Montana and other states. The "Corporation" buys and owns the RV, you just use it when you like, and can park it where you like. The "Corporation" lives in Montana, or Nevada, or someplace. You might have difficulty explaining it all to your insurance company, or if you get pulled over for some random reason. I guess if you have a rental agreement with your corporation as the lesse, and you as the lessor, it will go a long ways to explaining why you have California drivers license and work in California, and own property in CA, but are driving a RV with plates from another state, and has a different address than your home - the home that all of your other vehicles are located at.
Your insurance company might also ask "Where is your vehicle garaged?" or Where is it stored? That can be a problem if it is out of state, and more expensive if not at your home. And a finance company might have a requirement that you not take "Their asset" out of state for any reason. (while that does not make sense for a RV loan, it is probably in that fine print when you sign the RV loan, it probably says you may not take their property out of state without prior permission, or must keep it at home except for temporary time out of your driveway at night, say up to a maximum 30 days at a time away from your primary residence. )
Good luck,
Fred.