If you can live with them being FS98 vintage (and therefore framrate friendly, but a bit crude) then MDL2BGL available from flightsim.com (but I have a more recent version thats a pig to find on the net!) will do the trick. I think however SceneGenX actually allows MDL files to be placed in scenery as static objects but I could be wrong. If you do end up using old FS98 models it is possible to "replace" the old R8 format textures with bitmaps, so long as you keep the same filenames and internal texture layouts (mappings).
Been busy lately in real life so hadn't really had time to work on the airfield but now managed to get some free time to continue. Here are some shots on the progress so far. Have now managed to add trees to the scenery and vtp polygons on certain parts of the airfield. Hope you like