Trouble creating inside masks on surfaces

[jeff_rivers]

I'm modeling a couple different alternatives, and I want to make an inside mask on EG where my FG surface will be.

Is my workflow the problem, or are surface masks just buggy? 

I've created three EG surfaces, EG-1, EG-2, and EG-3.  I pasted the dref'd EG into each one, so now I have three copies of EG, one for each design option.  Each surface is on its own layer.

I have three FG surfaces, one for each design, FG-1, FG-2, FG-3.  I want to use the outer border of each FG in turn to make an inside mask for its respective EG surface. I can make one, masking FG-1 out of EG-1.  When I move on and try to make the mask for FG-2 to mask EG-2, no mask is created. 

Is it not working because I pasted the same original EG into each of the three EG option surfaces? Do I need to promote the original dref'd EG and copy it two more times, so each mask is applied to a completely unique surface?

[troma · Accepted solution]

What version are you in?
I believe in 2013 you can use one surface as a hide boundary for another surface. I've never tried it myself.

[jeff_rivers]

Further results- I've created three separate surfaces by first promoting, then making two copies of the original EG.  All three surfaces are identical, and occupy the same place in modelspace.

I still can only create one mask on one surface.  If I try to create an inside mask on either of the other two surfaces either nothing happens when the command finishes, or I get the error "Region ID already exists".

I'm concluding that only one inside mask can exist in modelspace within the boundaries of any surface, regardless of the number of surfaces.

Troma, thanks for the suggestion.  Hide boundaries seem to be working.  Per the help file only polylines or parcels can be used, so it won't be dynamic.  For this instance that'll have to be okay.

[troma]

Sorry I missed the 2012 in your signature line last time. The command I mentioned was new for 2013.