The problem is the preconception of what a base is. In Rust, building huge infrastructure was a great defensive tactic, as these buildings were more or less permanent and offered layers of protection for your stashes.
H1Z1 seems to be taking a different route (which I prefer) and has made bases smaller, less permanent establishments that you should expect to be regularly broken into (even after Tuesday's update). Building a huge base in the open just exposes you to an onslaught of raiders who see easy money... The assets of a whole crew contained in 1 space.
The people who dominate in H1Z1 will be small groups (3-5) who conduct planned, coordinated attacks. Who attacked us? No idea, it was over before anyone could see who did it. Where is their base? No one know knows, but my guess: It doesn't exist... It's a few small shacks, spread out and hidden, not a large structure of group of shacks. Something that doesn't draw attention to them. They operate as a network of individuals and duos, then come together as a squad when they see someone they want to hit.
After playing all weekend. my advice if you're struggling is this:
1. Shred your shirt and make a bow + 50 arrows. Go alone or with 1 friend and learn to survive, first and foremost. Individual survival skills are the foundation of a good team.
2. Attack the first person you see as a fresh spawn. It will teach you how to bow and fist fight, which is important even after you have assault rifles. Learn to kill naked.
3. Fighting zombies and the other players who are also fighting zombies is currently the best way to get loot outside of raiding shacks, though that may change.
3. If you follow #2, and learn to recognize signs of who is strong, who is weak, who may have something good on them, you will eventually kill someone and get a nice haul.
4. Once a guy has a sufficient stash, log him out, create a brand new "alt", and try to build a shed for the character who just scored a nice gank. Having many alts can effectively replace the sleeping bag the Rust players want.
Good luck, trust no one.