How could US customs check your car going into mexico? you pass through Mexican customs going into mexico, and you don't hit US customs until you come back into the US.
I'm not big into holding cents as they get to weighing so much. It takes a milk crate or a soda crate to hold a hundred rolls or so and it is tiring to walk up stairs or place them into a car to get them to the coin shop. I sell wheat cents as soon as I get a group of any size and convert the cash into silver or gold holdings. Much easier to carry and at least keeps up with inflation. I know that when my family has to handle my estate, God forbid, and they found buckets of memorial cents instead of a few gold coins, what a burden that would be to them.
That's what they make Mossbergs for. I'm thinkin I may roll mine or something. I have tons. I'm not really sure what to do with mine either.
I'm going to start using mine for magic tricks, I have these metal tubes that are air powered that I keep up my sleeve, then at the correct moment, I throw my arms up and press the button to trigger the air, and POW! PENNIES EVERYWHERE!