Are you a government employee or in the military? If so, you can get a regular non-live-aboard slip (waiting list) at Camp Pendleton's little marina (maybe...) or at Fiddler's Cove on Coronado Island (this is in San Diego where we've got a mooring at Fiddler's Cove). If you're active duty military, you can get on the waiting list for a live aboard slip at Fiddler's Cove but I don't know about Camp Pendleton. The waiting lists are long and the military marina slip situation isn't really set up for multi-hulls, though. You can get on the waiting lists for the moorings at Fiddler's Cove (where we have a mooring) which is a good option for a multi-hull. Sadly, there is no living aboard allowed on the moorings at Fiddler's Cove. Yes, we live aboard our boat now--we're hauled out in a boatyard--and we'll continue living aboard after launch, but we'll only be in San Diego a short time after launch and will spend most of it on the hook at the Cruiser's Anchorage or other (by permit) anchorages or moorings in So Cal. Working full time at Camp Pendleton, I don't think you'd have the flexibility to wander up and down the coast as we will, though.
On the other hand, regarding living aboard cheaply...You can immediately get on the San Diego Mooring Company's list (2 year to 8 year wait depending on which mooring field you're interested in) to get one of those moorings in the harbor. Cheapest way to go for a live aboard. By the spring of...2011 you could have a mooring...probably won't do, huh?
Oceanside has a small (small!) marina area adjacent to Camp Pendleton and waiting lists are likely to be long for just a regular slip (much less a live aboard slip). These folks in Southern California don't take too kindly to the whole term "liveaboard" for some reason.
Some of the higher priced marinas will work (down in San Diego) but they're all under the Port Authority rules of only 10% live aboards allowed. So, the quotas are met pretty quickly.
When we moved to San Diego to work on our boat (fall 2006) we also purchased a Rawson 30 to sail. There were no live aboard slips available anyway at that time, but we also learned that the marinas which had them were charging from $150/person ($300/couple) to $300/person for live aboard status. We rented a studio apartment for $650 and spent all our waking time either at work on the bigger boat or sailing the smaller boat
You'll find apartment rentals reasonable in Oceanside and what you'd save in terms of gas money coming up from San Diego harbor or down from Dana Point...it all helps out.
Do get on all the wait lists NOW not later. If you have orders to San Diego (military or civilian) you should be able to get on the wait lists at the military marinas now. If you're a contractor, you won't be able to use those marinas (I think)...