Hello all and hope your lives are full of creativity

I was wondering if someone can point me to a tutorial what will teach me how to make TRANS MATS for an outfit.

I would like to use this dress to make a 1940’s style high wasted half slip for a vantage style series I’m working on; the kind of half slip that would go under a high waste Pencil skirt

I at first thought I could just make the chest part invisible in Poser but it does not make the entire top of the dress invisible as you can see in picture #4.  So now I’m thinking that if I can make a Trans Mat that will start just above of the little decoration below her breast or maybe below, it would work ok for me.

Please can anyone direct me to a tutorial that can help me learn how to make Trans Mats?

type if skirt it would go under  

Thanks much

Steel