I get a lot of positive vibes from the ladies while driving but I can't say I've had OP's problem at work. It has never escalated pass smiles and flirting due to me keeping it short (but courteous) with everybody and using the boxes/diad to maintain distance between the customer and I. If you keep it professional, the customers will pick up on that and respond accordingly. By creating that fun atmosphere, you kind of opened up the gates to this.
Maybe next time you could use lighthearted tone and smile and say something like, "I'm going to have to start cleaning my truck's car seat so that my shorts aren't dirty by the time I get here." If that doesn't make them think twice about grabbing your ass, you got some real freaks on your route lol.