First, don't do the shadow wash until you've done your camo and added decals. You want to have this blend everything together.
Next, apply small amounts of thineed paint ONLY where you want shadows and allow capilary actio to draw the paint around. Never drag a brush with a wash over a model.
Do not, repeat, DO NOT apply copious amounts of wash then try to wipe off the excess, regardless of the FSM article to the contrary.
Doing this, you should be able to use any paint/wash combination.