if you don't need it to be solid you can also use moo mapper to raise the LOD level to.. w/e 50000 or something? but if you need it to be solid and have a COL then uhh... keep the LOD level under 300 and I think it was add a second dff into the .img *you can just add the same one again* and replace the 1st 3 letters of its name with LOD
I think, I'm not 100% sure, it's been a long while since I've done any of that stuff
or maybe there was info in the .cfg/.dat/ other data files? I don't have any gta's on here so I can't poke around for an answer :/ if you google for moo mapper tutorials about adding new models, you'll find what you need somewhere