My advice is purchase
the boat in Mexico but do not bring it into California until at least 91 days after the sale
is consumated. Have a Notario Publico notarize all the sales documents as well as any brokerage and financial documents as to where and when the sale was completed. Keep ALL receipts for moorage, slip rental, work done on the boat, take pictures regularly with a local newspaper showing the date the photo
was taken in Mexico, save all fuel
and personal expense receipts and be prepared to show this the the CA Franchise Tax Board to prove that you have kept the vessel outside of CA waters for the required period of time to avoid sales tax.
I purchased a boat quite a number of years ago in Washington
State, cruised up as far as Desolation Sound in BC for 4-5 months before coming down the coast. Sold the boat 5 years later in CA and they came after me after the sale alleging I bought the boat in CA. I had to fly back to BC and secure marina receipts, fuel purchase
and yard receipts covering the period 5 years after the fact even though the Bill of Sale plainly stated I had bought the boat outside CA. CA state govt could care less about your story if they can see a way to nail you. One error I made was keeping an empty slip in my name in San Diego
while I was away because moorage was so tight at that time.
As a result I have not bought anything in CA or traveled to that state even for a cup of coffee for several years now. Capt Phil