Hi!
I have never done a white coat - but I have a flak-p that I AM going to do one on...so I'm thinking about exactly this question!
I plan to use maybe a couple of white-shades in acrylic. I'm thinking a late-war vehicle in later winter with a patchy combo of worn white paint and a few bed-sheets... thinking that the tri-colour base should show thru in lots of areas.
Point being: vehicles came in all sorts of jobs- barely there to very complete white coats. You have a lot of options as to what, where, and how much!
I suggest look up some photos of winter panzers and form a vision of what you want your's to look like. Do you want a "fresh job", maybe a patchy last-minute mop n broom look, maybe a spring image with a mostly-trashed coat? You will find some example that will lead you towards whatever you wabt to show.
Depending on what you decide, recall that the white stuff was probably applied over a camo coat... And, if you decide that you want something less than complete, you'll want to consider where and how this base will show thru. I'm thinking of spraying my whites on sparsely over a complete tri-c job, and maybe washing some off in places, so as to try and capture what happens as the white washes off- maybe as if it were water-soluble or a "white-wash" product....
Cheers!
Bob