This is going to be a bit of a pain, but you could try importing your artwork
into a doom editor, then save that out as a doom type wad, then try to
import that with birgers' rott editor (under 'import' then doom.wad), if that is
successful, you could then save out everything as a rott file. You can get a
full featured doom style editor from here:
http://www.sbsoftware.com/
But what you really need is for a rott editor to see your artwork as things
that can be added to a level, and for that you would need the source code
to a rott editor, so your stuff could be included properly.
---------- Post added at 06:44 PM ---------- Previous post was at 06:40 PM ----------
The only other way as I've mentioned, is to replace currently existing artwork in the main
rott file with your artwork. You could use xwe to do the exporting/importing. But you would
have to keep track of the names in the rott file and you would also probably be limited
to the original sizes/resolutions of the original artwork that your replacing.