How to seal up decay around bilco doors?
I don't know how much time/money you want to invest in this project but two things are important, actually, three:


Water: Water is the enemy, so anything you can do to prevent introduction of water is key, it is the #1 solution and preventative measure
Rust: Unless you are going to sand (right down to the shiny metal), prime, and paint all and any areas exposed to the elements, rust will continue, even under a fresh coat of paint or any other sealant. So, weather stripping will NOT help, in fact, doing something like that on an already compromised surface will help it to retain water and rot faster
erosion: since the concrete has erosion, cracks, etc, mastic or any silicon sealant can delay continued degradation of the concrete, it will not stop it. Pay particular attention to my note in the first bullet, because any repair you make, you want to seal out water and tell the water where to go. Give it a path.


What you might do is replace the door, and get one that fits over the cement and just be sure to think like water &amp; gravity, and make sure you send it somewhere ... else.