All three of my buses have the BB body, and all of the doors work just the same. The 86 Jimmy has a (stock from the manufacturer) neat little keylock that is called a "Vandalism Lock," but it isn't really anything that would deter a determined burglar.
I LOVE the way the Ward buses' doors work....one in and one out, or two in, or two out....I've seen several variations on the same scheme depending on the size of the bus (long or short). They are no more secure than the other makers' doors, but they do provide more room to get into and depart from the bus. Close curb operation or in drifts would be difficult....
I may use a flat metal bar about 1/4 inch thick that will go all the way across the doors and secure with a large wing nut or hasp and lock arrangement when we are inside the bus. This is really unnecessary, as we always have at least one dog inside with us, and s/he will alert John Colt of anyone who approaches.
Unless there is something within you that is above you, you become lost in those things that are about you.