Can't create rmesh of room b3d file.

Hello! Oh right so I'm trying to create my own mod (nothing to special, mostly a reskin) and I was trying to do small modifications to few rooms. Nothing too special, few extra texture placements, removing some props etc. So I open rooms in fragMOTION using Juan's plugin, then export them to b3d, and trying to convert them using Rmesh Converter. Now, for some reason Converter always creates a 1kb file (rmesh) that is apparently blank (both ingame and in fragMOTION).
I tried doing the same thing without modifying anything, just exporting file as b3d and then converting but it doesn't work either. I tried replacing room paths in rooms.ini to open .b3d versions of the rooms, but then same thing happens - rooms are blank ingame. I saw a similar thread asking about the exact same issue, but it had no replies.

The other thing I figured out is that upon converting room to b3d, placing it inside with texture images and opening it using fragMOTION, textures appear with black stripes all over them. Juan once said that without using 3D World Studio the lightmap info is lost, is that what's causing it? And if so, is there a way to modify rooms outside using 3D World Studio? I just want to remove few props and that's all. Can somebody help me with Rmesh Converter issue?