I'd recommend trying a clean blend as the only mod needed for bass. Alternatively the Ruetz mod can be helpful as well but it changes the character of the distortion some.
Also just going to plug this project as I think it's the best rat-based bass distortion I've heard.
-OR-
Use the values from Proco's Juggernaut View attachment 9542
Though, the RAT is already pretty awesome on bass, as is. Just listen to some Jesus Lizard