Everybody who plays Rott using external .rtl files has to go thru SETUP which is a pain in the butt. I've written a batch file which automates the process and removes the pain (but not your butt hopefully).
After downloading play.zip, unzip it into your Rott directory then just type play [.rtl filename] [.wad filename]
eg to play a file called myfile.rtl you would type
play myfile
to play a file called myfile.rtl with mywad.wad type
play myfile mywad
as simple as that. No extension is needed altho it doesn't care if you do add it. If the file is not there then it'll tell you and bomb out.
Things that can go wrong:
All the files in this archive MUST be in the Rott directory 
If the .rtl file you want to play is in another directory then you must specify the pathname on the command line
eg if myfile.rtl is in a sub directory of Rott called RTLS then you would type
play rtls\myfile
if mywad.wad was in a subdir called WADFILES you'd type
play rtls\myfile wadfiles\mywad

Hope this simplifies your Rotting

Les Crockford
les@highway1.com.au