The most important thing about bunkers is getting that initial design right cause it sets up everything else. I've found the stability bunker is probably your best bet when starting out, its really solid and not too hard to build once you get the hang of it. Just place two foundations next to each other then add those triangle foundations on the sides and upgrade them to metal, that'll give you good protection against raiders trying to get sneaky with the soft sides.

Something interesting i learned is how well triangle elevation bunkers work for smaller groups. They're pretty neat with those stacked triangles and half walls, makes it really easy to hide your loot vertically which is super helpful when you're tight on space.

The doorless design is actually my favorite trick, since raiders usually expect normal entrances. You basically work with the roof mechanics to get in and out, and make sure to reinforce those critical walls with metal. Its a bit tricky to build at first but definitely worth learning.

For general protection, i always tell my teammates to focus on the metal upgrades for the important parts, and don't forget about those backup tool cupboards. The whole honeycomb thing around your main structure is super important too, even though it uses up more resources than you might expect.

Good to know: one last thing that's really helped me using garage doors for your internal security layers works great, and setting up some decoy loot rooms can really mess with raiders. These setups usually force them to burn through like 20 40 rockets depending on how you build it, which is pretty solid protection if you ask me.