They work when you have the right stuff for them, especially when you start off with worldfinals's.38 version of SMV4. (which is right here.) In regards of the add on trucks, you can go with two choices, one being easier than the other: One being to extract each truck zip into the folder, which makes hunting down parts extremely easy, or you can just place the zips into the folder (which is the approach I went with), but it makes hunting down certain parts that could be missing on trucks difficult.