Generally, you want to bulletproof your base to avoid raiders from shooting you from outside through walls and such.
Note: Bullet penetration applies to the width of a prop, not prop specific.
Few list of props with their advantages:
2 x 2 Block (models/hunter/blocks/cube05x05x025.mdl)
- Blocks penetration from most weapons, such as: Pistols, Shotguns, SMG's, Rifles, and Sniper Rifles.
4 x 4 Block (models/hunter/blocks/cube1x1x1.mdl)
- Blocks penetration from 2 x 2 Penetrations and explosives.
What to block:
Walls
You want to try to block any world walls you may believe that has a thin thickness to it. Remember, penetration is applies by the width of something.
Ceilings & Grounds
Same rules apply here as for walls, but only if something below or above has an existing space.