There are some definitive laws that assist us nomad-types, namely the Federal Laws of transporting a legally owned firearm across state lines and into each state. The NRA has the most information out there at easy reach --
https://www.nraila.org/articles/20150101/guide-to-the-interstate-transportation
In short, it is 100% legal to own, and travel with a gun, even using air transport. I have traveled with my guns through dozens of states (including CA) and even gone through
Canada with multiple guns, and had my pistol shipped to Alaska during my time up there, all perfectly legal. I do however avoid states with stupid-restrictive guns laws except CA where I have no choice thanks to my family's refusal to move out of that damn place.
Others choose to store their guns when going into countries that do not permit us to have our guns... such as Mexico, where I am now. You can store guns at local firearm dealers for a nominal price, however you must know that a firearm dealer can NOT return a handgun to a non-resident of the state the dealer is in. For example, if I were storing my pistol in Southern California while I went into Baja, he would gladly take & store my pistol, but he could not give it back to me. He has to ship it to Colorado (where my ID says I live) and only a Colorado firearms dealer may hand me my pistol back. To get around that is to simply rent a small storage space and store your own weapons in your own rented space. You effectively never lose possession of the firearm and do not have to worry about taking possession again.
California specifically has many (many, many... MANY) gun laws. The ones that effect us the most is that the gun has to be locked in a container in a separate compartment from the driver, AND the ammo needs to be in a locked container in a separate compartment as well. On top of that, California has a magazine-limit-law. Anything more than 10-rds is illegal in the state. The way around that is to dismantle the magazines into their separate parts while in the state. I still lock them up to be double sure.
California also has an "assault weapons ban" which goes beyond any other state. It now includes ANY rifle with ANY detachable magazine (which is pretty much ALL semi-auto rifles). You are allowed to transport the gun *through* the state thanks to the Federal Laws, but if you are *staying* in the state (beyond a hotel in route while passing through) the state laws forbid the transport of any assault rifles other then too a shooting range and back to your home. You are not allowed to just have one in your vehicle just because you own one.
California's laws are some of the most restrictive in the country, but many states nearly mirror many - if not most - of CA's laws. New York, New Jersey, Massachusetts, Illinois, DC, and Hawaii are just a few of those states that have most of the same laws that CA has.