FOR AMATEURS OUT THERE LIKE ME! READ THIS!
I have finally discovered how to make this thing work. NO MORE BROWN BOXES. It is very important that you read the documentation, it is long, I know, so I will try to simplify what I did.
I installed the RTMTV3 folder in the plugins folder (my documents/simcity4/plugins). then read the ReadMe file where the dependency files are listed, you need to download the models you like, all the dependencies links are provided, YOU DONT HAVE TO DOWNLOAD THE ONES YOU DONT WANT, and for simplicity, don't download more than one type of model, for example, download only one type of bus stop. Put the downloaded files anywhere in the plugins folder (put them in subfolders if you like).
Then basically what you need to do is delete a bunch of files. in the InstallationExamples file, you will find 4 examples, I left my main RTMTV3 folder exactly like the first example (once again, this is done by deleting the rest of files that dont appear in the first example). Then open the ReadMe file and go to dependencies, and look up which file you must have in the "Props" folder for the model to work, and then delete all other model types. For example: to select the [color=#000000][background=rgb(224, 208, 192)]Ninja's BusSign Model,[/background][/color] download the dependencies into the plugins folder, then go to the "Props" folder and you will find three .dat files that begin with "[color=#000000][background=rgb(224, 208, 192)]RTMTV3_Prop_BusSign_[/background][/color]".. you want to use the "Ninja" model type so delete [color=#000000][background=rgb(224, 208, 192)]RTMTV3_Prop_BusSign_TfL.dat [/background][/color]and [color=#000000][background=rgb(224, 208, 192)]RTMTV3_Prop_BusSign_TH.dat[/background][/color].. leaving only [color=#000000][background=rgb(224, 208, 192)]RTMTV3_Prop_BusSign_Ninja.dat[/background][/color].. Do the same with the other models, and you're done, no more brown boxes! Take into account: in some [color=#000000]tables, the single prop implementation are coloured [/color][color="#662020"]BROWN[/color][color=#000000], and the prop family implementations [/color][color="#006600"]GREEN[/color][color=#000000]. Please install either implementation, BUT NOT BOTH![/color]