At this time there is no easy method of changing the default URL for the vehicle listings. However we are working on adding an inventory shortcode feature that will make this very simple, unfortunately I don't have a clear timeline on when that will be available.
One option might be to use a "redirect" PlugIn and redirect yoursite.com/inventory to go to a vehicle search results page. I'll be the first to admit that isn't a very good solution, but short of getting deeply involved with the code I think it's currently the best option.
I hate to give you even more bad news, but at this time there isn't an easy way to change the vehicle options either. What kind of options would you need for RVs? If you post a list of them I can try to make sure they get added to the list of available options in a future release.