OK I'm Stuck what do I do now?

Ok I have got all of the trim for the hatch dry fitted and I am ready stick it down what do I use?
Silicone, Polyurethane or 3M 4200 sealant looking for something to stop the water from traveling under the trim. It doesn't need to glue it down the screws will hold it. The manufacture of the Fantastic Vent recommends silicone. The blue box store likes silicone as well. I decided I only want to do this once so I'm putting it up for a vote. Please tell me the pros and cons. Here is the link to my build journal so you can see what I'm talking about.
http://www.tnttt.com/viewtopic.php?t=29303
Silicone, Polyurethane or 3M 4200 sealant looking for something to stop the water from traveling under the trim. It doesn't need to glue it down the screws will hold it. The manufacture of the Fantastic Vent recommends silicone. The blue box store likes silicone as well. I decided I only want to do this once so I'm putting it up for a vote. Please tell me the pros and cons. Here is the link to my build journal so you can see what I'm talking about.

http://www.tnttt.com/viewtopic.php?t=29303