What we are going to build is a simple yet efficient "Air Lock" system for your base entrance. I'll show, step by step, how you can do it and the advantages of how having an Air Locked base can help you survive in the cruel, cruel world of Rust.

Firstly, you will need 2 doors. The doors need to be placed as following (the second door can also be on the right, or left, but never in the middle):
 
 
 
 
The placement of the doors needs to be like this, so they are close to touching each other:
 
 
 
 
If you have done it right, the inside of your base should look something like this:
 

Once the airlock is built, just keep the doors open like shown below and your base should be unreachable from that point of entry.
 
 
The strategic defensive bonus that the airlock gives you, is that you can shoot through it.
 
 
Basically, the person that defends your base (if you're playing with friends) can see incoming raiders from a mile away and is able to get the jump on them. Even if he dies, staying a little away from the doors will make the body unlootable by the raiders, because it will be too far away.

I hope I could help you with securing your bases better, this was my first guide, so thank you for your attention!

Special thanks to TrapGod for helping me with creating the guide