Mud in fender with pinch weld mod

Hey guys so I've been having this problem with the pinch weld mod where whenever its a little muddy the inside of my fender and the door jam area get mud built up. Here's the cutting I have done, and ideas to remedy this?

 

Flex seal

 

Problem is, and the picture doesn't show it, but there is about a .5 -1 inch gap between the fender liner and the back part.

 

Hey, you could try some expanding foam also called foam fill, just get the minimal expanding type, Walmart should have it or Lowes, just wear some gloves because it's hard to get it off. Then trim the excess off the next day and spray it black.

 

Some of that foam will be melted by spray paint FYI

 

That's right you need to get the exterior type that is UV protected and safe for most paints.

 

Duct tape