Hey Godvin,
what we actually used here in the past (when 3/4 masks became famouse) was a leather collar (from neck to nose) or a "cloth scarf or tube" to cover the complete neck and mouth with it. Although most of our mounthless modles used to cover the neck.
Another option is to stitch or glue the mask on a faceless balaclava. However you will always need build something to cover the neck. to make it better looking you can put latex on the balaclava and paint it in the mask color. (keep the cloth stretched while doing this otherwise you'll get problems when trying to put it on next time, as it becomes very inflexible even with few latex on it
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)
What additionally helps with the balaclava is to makup the mask around the mouth in order to cover the transition between skin and mask.
Most powerful is a combination of all 3 options or you directly advance to the best option and buy a full mask
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i.e. from Wendy 200 - 250 € atm :
http://forum.orklager.org/viewtopic.php?f=119&t=11539