XML Effects and Triggers

Hello all, I've been running searches on Google and here for two days now and I have not found an answer to this question or any examples; has anyone had any success, in the new FS9 XML format, combining effects and triggers? For example you have a forrest fire and want to add a thermal due to the fire. I can add the fire and I can add the thermal but the thermal is there all the time even though the fire is only there during certain dates and times. I would like to combine the two. When I try it refuses to compile. Any ideas?Chris