[ferretchucker]

Well if you did it as though the characters were making a video diary in between whatever was going on, then you could cut that into the trailer. Gives information on what's going on and maintains the feel.

There are little things that I always think make an amateur picture (trailer or not) seem amateur. One is background noise. Professional productions have so little background noise. In particular there's stuff like the hum of the machine, wind in the background.

Also, something that might help give it some gritty atmosphere is to subtly raise the contrast but lower the saturation.