If the swivel is a plate type (two round plates with a pivot in the middle), try drilling a small hole through both plates in the closed position and dropping a pin (small nail or screw) down through the hole to hold it in place. This assumes that the mechanism for yours is accessible in the travel position, not sure what it looks like.
2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2012 Chev Traverse LT with TP