There have been a few threads here about retrofitting RV door latches onto CT doors:
http://www.mikenchell.com/forums/viewtopic.php?p=357531&highlight=#357531
http://www.tnttt.com/viewtopic.php?t=36645
The best solution that I saw here for how to prevent someone from locking you inside your CT was the person who put an eye hook on the wall of their trailer, to lock the handle to in the open position. The simplest solution was as someone pointed out in one of the threads above to put the lock back into the hasps after you open the door, since the same hardware that prevents the handle from being opened can be used to keep it from being closed. I have my doubts that someone could force the door open from inside should someone just put the cam lock bar close to the locked position, hence the latter not being the best solution.
When I picked up my trailer last month, it came with an RV lock and no cam lock bar. The dealer stressed to me that I should always make sure that the deadbolt is engaged when towing, because RV locks apparently have been known to pop open on the road at times. Judging by how the commercial shipping industry and CT manufacturers have standardized on bulky cam lock bars in times when shaving every penny/ounce of weight from a vehicle is important, I would say that they haven't found a cheaper way to hold the doors closed that doesn't have problems if the trailer flexes.....