It's only a virtual train, what difference does it make whether it has a watermark, or what quality the recording is ? You're not going to get an Emmy for Trainz Movie Making, so use a free recording program
First off: If you examine TV and movies, you will notice that they change the view of the camera @ every 5 seconds, so viewers do not get bored with a lengthy scene. Nothing is more boring than viewing a train coming down a track from infinity focal point, taking many minutes to get to the crossing, then the horn blares so loudly blowing out your sound system, then you see and endless boring parade of 137 railcars speeding by in a blur ... Better to use free Fraps/Bandicam and import the movies into MS MovieMaker, to splice together hundreds of 5-10 second clips, making a more interesting movie ... move @ 500' down track from the crossing, and @ 200' back from the trackside, and use rotating trackside cameras which are elevated on a slight downward angle, looking down from @ a 10' height