I love rustic weddings, they warm the heart and create such a lovely environment its hard not to have a good time! While it might not be the traditional opulence of a ball room, there is a rustic opulence in rich fabrics and fine details. The beauty in a rustic wedding is that both ball gowns and or fitted gowns are lovely. You will be hard pressed to find a shape of bridal gown that wont work, but make sure you choose fabrics with texture like organza, lace, dupioni, taffeta, chiffon.. stay away from duchess satin, the shine will contradict the feeling of the wedding. At a rustic wedding a story can be told with each detail and photo taken, when you are planning or dreaming of your rustic wedding think of the hidden or quiet details and make those a focus. You will surely capture many ooh's and ahh's from your guests.
Have fun planning and don't forget to use textured fabrics for your gown!