I live in south OC (on border of SJC and San Clemente) about halfway from L.A. to SD. I would say that about 90% of the professional football fans here are all Charger fans. And the further south its 100%. I've taken the train to SD to see a game and its only about an hour. It's also quite a fun ride when the Chargers win-and even when they don't. Lots of party folks-those Charger fans. The Charger fans I'm acquainted with are all planning on driving to L.A-like me -or taking the train up from further south. Add to this the fact over the last several years the Chargers have been a far better football team. Should they continue to be better-well you know what will happen (i.e. the reverse of what you saw last year near the end of the season in the Coliseum). In sum the Chargers have a very strong fan base and from what I can tell that won't change with their relocation.
I just hope the Rams do better than the Chargers so I won't be bombarded with insults here.