Depends where in the world you are and from which country to which you are travelling.

I have had no trouble moving around West Africa, not even 1 vehicle search. We had a little search leaving Morocco for Spain but that was just external and he took one look in the back and waved us through.

I dont think many locals know how much currency overlanders travel with making 'looking for safes' a bit obscure to them. Your more likely to get stuff nicked off the dash whilst being distracted than having your secure storage found and raided.

G