AAA digest of travel trailers and laws regarding weigh stations.
http://drivinglaws.aaa.com/laws/weigh-stations/Info for Canada at the end of the list.
It's geared more for the RV RV trailer.
As I thought, Iowa is all vehicles 10,000lbs and over must weigh. Used to be 6,000 lbs but vehicles like the Hummer H1 were over that and really should have been stopping at all open scales.