Thanks for the information guys. Although my truck is licensed as a commercial vehicle I don't think I will do it anyway. It will void the warranty on the 5th wheel also.
I know when I looked a year or so ago I found this:
"Cars, passenger vans and SUVs are not permitted to tow more than one trailer or one vehicle. Motor homes, trucks, pickup trucks and truck campers are legally permitted to tow two trailers or a trailer and a motor vehicle behind a trailer. However, a three vehicle combination that is swaying excessively, is unstable or has reduced handling capabilities is subject to action by the police as an unsafe combination of vehicles under the Highway Traffic Act."
I printed a copy for reference. Obviously the law has recently changed.