AE : Using a drawn brush as a mask Is there a way to mask brush strokes like you can with a pen?

At present, Im using a pen to create a mask then generate a stroke (Effects>Generate>Stroke). 

I then use reveal putting a keyframe on the end of the effect to reveal the comp following the pen's stroke if that makes sense.

I want to use the same type of effect by revealing a larger background image, but the stroke's maximum width using the above technique is 50 which is not big enough.

From what i understand, brush strokes are vectors in AE so is the same type of thing possible using a brush to create a mask?

thanks
If you use the brush on a layer, it actually applies the "paint" effect to the layer. If you paint on a layer with the brush and expand the properties for effects>paint>brush 1> you'll see that there is a start and end setting that can be animated, allowing you to animate the stroke.