ST tires have marked on them " not for passenger vehicle use" Now there are a number of states that allow passengers to ride in a trailer while being towed down the road . ( I wouldnt do it but it is legal in some states) If that trailer has ST tires on it , the driver could be ticketed for allowing passengers to ride in an unsafe vehicle .( ST tires are not for passenger vehicle use )
In Indiana , it is legal to ride in a 5th wheel , travel trailer and a truck camper . And Indiana is the state that produces the most campers , so by Indiana law a 5th wheel or travel trailer is a passenger vehicle , so any built in Indiana should leave the factory with tires capable of carrying passengers . Basically it is probably illegal to run ST tires on a travel trailer .
14 states allow it in 1 form or another
http://camping.about.com/od/frequentlyaskedquestions/f/Passengers-In-Campers.htm