Rick, that is excellent, you should have seen my first attempt!
As you have asked for suggestions, I hope the following might be of help.
I briefly looked at those mask thingies when I first thought about having a go at this type of cammo., but decided it would be too messy and awkward working around all those protrusions.
So as I just brush paint I ended up doing mine freehand. Taking a suitable sized old paint brush I cut the bristles almost down to the ferrule then with the smallest amount of paint on the brush I just touched the plastic and sort of twirled the brush to get a ' disc'.
Here's three I did. All prior to weathering etc.
1/35
1/35 Stug
One of those 'Two in a box' instant 1/72 tanks. Spots a bit big. All part of the learning curve.....
I hope you don't mind me posting the pictures but probably better than me burbling along trying to write what I'm getting at.
My method might be worth having a go at and might help to keep your sanity!
Good luck whatever method you adopt and I look forward to your Ardenne diorama.
Cheers.
Ron