After doing much research on this subject the only preventive measure you can take to help prevent an evaporator corrosion pinhole leak is to replace the A/C dryer on a regular basis to help keep the R134a and system DRY. CryoSeals, TuneAir {
www.cryo-chem.com} is a special agent on the market {TuneAir is not a sealant but a special dryer chemical charge} you can add to your 134a that converts any moisture in the system into a harmless substance. Keeping moisture out of the system is the most important issue, period. Any moisture will become acidic and slowly corrode pinhole leaks in the evaporator over time, because aluminum was use to make the evaporator. You cannot prevent joint cracks leaks in an evaporator that can develop due to stress.
I would guess that people who live and drive in high humidly areas like Florida, Georgia etc. have a higher failure rate than those who live in say Arizona with relative low humity. Moisture via humity will make it's way into the system over time.