Jeff,
The USPS seems to be inconsistent in regards to the customs form. I have only had to fill it out on larger packages of chips. Usually packages of up to 1-6 chips I have not had to use the form. Just depends who is working the window at the time. Same goes for the 1oz surcharge for "oversize". Most clerks charge it. Others test it and only charge if it will not fit thru the test slot. I have also had one package that was tested returned to me for insufficient postage because the clerk on duty did not charge the surcharge. I was pi**ed. I would rather pay the charge than have a package returned. Good luck with your sales.
Paul