You sure it was a movie? This sounds like two anthology tv episodes. One was an episode of either tales from the darkside/monsters, where the man is a bible salesman, and has to sleep in a room with the daughter, with only a modesty sheet between them (the daughter looks really attractive at first, but turns out to be really ugly at the end). The second, an episode of tales from the crypt, was called "Death of some salesman". It featured pretty much the same senario, only this time the girl is ugly right from the start, and the entire family, mother, father, and daughter, are all played by Tim Curry (the salesman might have been Ed Begley jr, but dont quote me on that). Then again, the whole "shotgun hick wedding" is a long running cliche, so it could have come from a lot of places.
