I'm trying to use SilverStripe as a listing/search for car parts at a scrap yard. I'm new to SilverStripe for this kind of application so I'd like to know the proper way to model this.

Each part has a make and model of the car it belongs to. I have these stored as relations to Make and Model objects so the client can add/remove new makes/models. I want people to be able to filter makes and models with the drop down in the search form on the frontend but I can't seem to find a way to modify the search form fields for a related object to be anything beyond a text input. I've noticed that db fields of type Enum behave this way (with a dropdownfield) but an Enum is clumsy when I have 100's of models to list.

Please forgive me for sounding needy, but I'm interested to see how you get this working. I just started an attempt to create a search using search context (http://silverstripe.org/general-questions/show/272699?showPost=272699), but I am lost on how to continue. Your solution can either help or address yet another type of search I need to implement on my current project.