Hangars at popular airports in So Cal regularly change hands but you usually have to be on the inside track to even know of one coming available before it’s gone. They are often sublet so their availability isn’t on any list. FWIW he might look in the rural desert, places like Mojave and adjacent airports, Borrego, Imperial, Brawley and so on. Or Hemet. There’s more likely to be a hangar available at a reasonable cost, and as a side issue the drier air is also good for the plane in storage.
I have a friend who is planning to fly his Mooney from Europe to Oshkosh, then to the west coast, which will allow him and family to take repeated non-stop airline round trips for Mooney flying around the western US before he eventually flies it back to Europe again. He needs the plane to be within striking distance of a major west coast city to make that work and I’ve suggested the same to him. I would fly him to his plane after his arrival in the area.
I assume your friend has the Annual Inspection figured out for a year long stay - that might be an issue for a French registered plane stored for a year in the US. My contact’s plane is on N-register and we have an A&P IA available who speaks the same native language, which is helpful.
