You can edit the .opt file yourself, and add the stuff you need. The instructions on how to do so are in the boom.opt file, so take a look at that and try to work it out. If you're still stumped, send me the .opt (pm or post here) file and I'll apply the changes I made to an older .opt file, assuming it still works. Then it should work for you.
Making a 3-D floor using DeePsea 12.13 is quite easy. You don't need to edit .opt files or write scripts or anything. Make a room. Make a sector in the room where the 3-D floor is going to be located. Make a sector OUTSIDE your map. Set the Ceiling height (of the secotr outside the map) to the top of the 3-D floor. Set the floor height to the bottom of the 3-D floor. For instance, if you want a 3-D floor to be 16 units high and the top of it at 64. Then set the sector ceiling height to 64 and the sector floor to 48. Remember, the ceiling texture is the texture that will appear on top of the 3-D floor and the floor texture will be on the under-side. Then [Right-click] on one of the OUTSIDE sectors linedefs. Click on the 'type' button then select 3-D floors (item J) then choose the only item available (for now) the
sector_set3dfloor +Tag-3Dtype-3Dflags-Alpha-TagHi . Then fill in the items in the pop-up box. Linedef tag is first, then the 3-D floor type. Use 1 for a solid floor, then for Alpha enter 255. This is the translucency of the 3-D floor. 255 is 'none'. Then click 'OK'. Change to 'sector mode' and go to the sector in the room and tag it the same as the linedef you just set up. That's basically all there is to it! Save your changes and test the map. Your 3-D floor should appear. There are other settings for the 3-D floor type & Flags. You can get them in the documentation area of this site. Also a thread on the TagHi item is in the GZDoom area. It is used to set tags higher than the 255 limit. I have been using DeePsea for quite some time and am pretty familiar with it. Let me know if this helps you. Now if someone could help me with sloped 3-D floors!
I forgot to mention that the texture of the sides of the 3-D floor will be the same as the texture of the Tagged linedef on the sector OUTSIDE your map.