Probably several ways to do it. I did it the old fashion way...
1. draw 4 new lines on the top side (trace on the existing edges).
2. make a new Network Surface with these 4 new lines (because Network Surface doesn't work with the edges/lines in the original file unless I explode/ungroup/something).
3. draw new 6 lines on the bottom side (trace/follow the existing edges.
4. draw another 1 line across the middle of the 6 lines set.
5. make a new Network Surface with the 4 lines ("half" the bottom).
6. make another new Network Surface with the other 4 lines (other "half" cover/surface).
7. move all the leftover text/lines (not surfaces) to another new temp layer and hide these lines (or just delete these lines/etc).
8. right-to-left mouse sweep to select all these surfaces.
9. do the Sculpt thing and voila ... now we have a solid.
10. run the MASSPROP command on that solid and we'll have something in the attached file/picture...
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