I would just point out that before you "fib" on your California DMV forms on what you paid for a vehicle, just keep in mind you are committing several prosecutable felonies when you do that. And what I mean by prosecutable, is if you are caught they WILL prosecute you. Just keep in mind that the person you bought it from will submit a Release of Liability form to DMV and they are required to report the price they sold it for. There is no motivation for them to fib as you're the one who will be paying the taxes. So even if you can convince them to fib, when the DMV Investigator (Fully trained detectives that work just for DMV) comes knocking on their door and asked them to provide a statement under oath about how much they sold the RV to you for, they are going to squeal like a pig on you and cut a deal to keep themselves out of trouble.
I once save a relative of mine who got a vehicle from a family member out of state and did not change the registration on it. One day he got a letter in the mail from DMV saying he needed to come change the registration and put California plates on the car. So he had the form and the form said either pay a penalty for not changing the registration in 10 days, or sign this form under penalty of perjury saying the vehicle first came into the state less than 30 days prior. Luckily he called me. I asked him how did DMV know he had the car at his house. He said he didn't know. So I told him how they knew. A CHP Officer had spotted the car and made note of the plate and location. They then checked on the car over a period of several months and knew good and well it was still in the state. So if he signed that form and sent it in they would prosecute him for perjury. So he didn't do it and confessed to how long the car had been in the state and paid his penalty.