Using a voltage regulator

Background: I live in Mexico. We suffer from a highly fluctuating voltage system. I have put voltage regulators on all sensitive electronic equipment (refrigerator, microwave, washer, dryer, computers, modems, routers, etc.) but use an S 15 APC surge protector on the stereo system.

Question: Since the APC a surge protector but NOT a voltage regulator would it be wise to put a voltage regulator between the wall outlet and the APC? Currently I have to set the high end of the APC to 135 volts to prevent it from constantly sounding the alarm and going to battery back-up.

We also suffer from brownouts which can be just as deadly to equipment.