var FileWriter writer;
.....
self.writer = self.Spawn(class'FileWriter');
self.writer.OpenFile("MyFilename", FWFT_Log, ".txt", true, true);
.....
self.writer.Logf("My Text Here");
.....
self.writer.CloseFile();
Logf is probably pretty slow, so it may not be a good idea to write something every tick
But I guess, you need something into file on round start/end.