winter camo was (and often still is) a temporary application over the original camo paint job. The paint may have been logistically supplied to be applied by brush or spray gun, or may have not been much more than white housepaint scrounged from a barn and slopped on with a mop. White sheets may be used to break up the outline , but that would not be very durable. Shep Paine's books on military modeling cover this subject well.
The temoporary and often thinly applied white wash will wear away leaving the original paint underneat exposed. There are several ways to acheive the effect, including painting and sealing your oringal camo with Dullcoat, then applying an acrylic whitewash over the top. I watched in amazement as a fellow modeler did this at a club meeting, and when the white acrlic was dry, he took a rag dipped in alcohol and wiped downward, streaking the white as if snowmelt and ordinary wear wore off the finish. The final step was to apply a VERY thin filter of Prussian Blue oil as well as complimentary washes of umber, etc. The wonderful thing about snow camo is the way you can weather it, since the white paint will pick up all sorts of grunge, soot and grime from the crew and ordinary operations.
good luck with it
David
Build to please yourself, and don't worry about what others think!
TI 4019 Jolly Roger Squadron, 501st Legion