Dan, I have been playing with the weathering stuff for years now, and I have had very good luck with mud effects, even heavy effects without any trouble at all. Thing I do is lightly oil any moving parts before applying the mud effects. Suspension pivot points and such, so there is nothing stuck there to prevent movement. Trick with this type of stuff is do it in layers and slowly build to the look you want. It adds the depth and feel for real mud and dirt. And if anyone can do it, you certainly can, man.