We have five kids, and not too long ago drove from SA to QLD.
We were actually turned away from 1 hotel (at midnight!!) because, and I quote: "We don't have a room.. for all of YOU"
Hmm. Needless to say, we kept driving (exhausted) until we found a caravan park. Woke the manager, and stayed in a cabin, which was much more comfortable than that sinky motel would have ever been. \/
Cabins are the way to go.. definately.