Just bought a toy hauler almost brand new. Put my bike in back and tied it down with 4 straps so tight it was like it was welded to the floor. 40 miles later I stopped at a rest area and checked on it. It was over on it's side with the handle bar going through the wall...
I have always used a wheel chock and never had any problems but I just bought this away from home and couldn't put one in till I got home. It now has a harbor freight locking wheel chock.
Unless you want to destroy your bike and toy hauler a locking wheel chock is the only way to go with 4 straps.