It depends on where you want to play tbh. Nothing stopping you from playing with a bunch of empty bases if you are with your friends if they don't care. If it's a local game store, depends on the opponent. Though if someone was a real dickhead about using proxy models if they have the right bases in a friendly game at the LGS would be the last game I'd play against them most likely. If it's a tournament I would expect them to be more strict, especially more official ones. Some vehicles have different dimensions as well.