The dirt/mud is done on the lower hull... I think.
For the mud, I used Ammo of Mig acrylic diorama effects to serve as the base and to build volume. On top of that, I added multiple tones of Ammo enamel effects and topped it off with speckling for even more variance. I feel like there's more I could add but I can't quite put my finger on it. I also added some grime on the roof of the fighting compartment using oil paint rendering, which turned out okay I suppose.
I'm getting excited because I feel like this is getting ready to cross the finish line!