Colissions were, and may still be, a function of polygon density. If the ship gets too big and the polygons too massive, strange things can happen, though I'm honestly not sure if that's a problem with the model or the converter. There was a time too that FS2 had a clipping plane at 100km from the player, which would be a very bad thing for ships larger than this boundary, though that's been moved out beyond reason. However, if you want this model just for scenery, I don't think it's a problem if it's huge. Bigger things have been put in-game, though they weren't nearly as complex.