So there are 2 fees to worry about....
In California they call it Sales/Use tax so for example..
This a charge assessed against the purchase price.
so if you live in Los Angeles County some city charge at a rate of 10.25%.
Sales tax is set and approved by voters in elections.
but tax is only charged against a purchase.
each year in addition the DMV charges Annual Registration fees.
Some years back our Governor was Grey Davis and he had approved the increase of vehicle registration fees about 2.2% each year.
He got Recalled and Arnold Schwarzenegger became Governor and reduced the car Registration tax to under 1%.
Back in 2017 Governor Brown increased the car registration fees again.
SO if you buy an RV in a 10.25% city/county sales tax area then you could end up paying 13% in Governmental fees combined at purchase and then the DMV registration again each year in California.
California has a way around this if you buy an RV.
here is an example:
If you are a able to buy your RV in Full and you want to buy from a California Dealer this is the way to avoid tax..
At time of sale the dealer can drive the RV under dealership control outside of the state across the state line to someplace like Phoenix, Las Vegas are any nearby city that is outside of California. Once the dealer has driven the RV across state lines the nature of the transaction changes from a retail transaction to an interstate commerce transaction.
You the buyer and the dealer rep need to visit a Notary to sign a California tax form CDTFA-448.
The Notary provides 3rd party verification that the dealer appeared outside of California. The dealer can accept and retain this completed form instead of the tax money.
then you the buyer can go register in Montana or somewhere much cheaper. If you the buyer keep documents that the RV was outside of California 51% for the first year then you will not have to pay tax to California even if you were challenged by state tax audit.
The state publishes a manual for Auto dealers to understand the complexity. but anyone can download and read it.
Publication 34, Motor Vehicle Dealers - CDTFA - CA.gov